TheInfoList

Petroleum (), also known as crude oil and oil, is a naturally occurring, yellowish-black
liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, and ...
found in
geological formations A geological formation, or formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguish it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exposed in a g ...
beneath the Earth's surface. It is commonly refined into various types of
fuel A fuel is any material that can be made to react with other substances so that it releases energy as heat energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but has ...
s. Components of petroleum are separated using a technique called
fractional distillation Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation to fr ...
, i.e. separation of a liquid mixture into fractions differing in boiling point by means of distillation, typically using a fractionating column. It consists of naturally occurring
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarb ...
s of various molecular weights and may contain miscellaneous
organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organi ...
s. The name ''petroleum'' covers both naturally occurring unprocessed crude oil and
petroleum product Petroleum products are materials derived from crude oil (petroleum) as it is processed in oil refineries. Unlike petrochemicals, which are a collection of well-defined usually pure organic compounds, petroleum products are complex mixtures. The ...
s that are made up of refined crude oil. A
fossil fuel A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms, containing organic molecules originating in ancient photosynthesis that release energy in combustion.Schmidt-Rohr, K. (2015). "Why C ...
, petroleum is formed when large quantities of dead organisms, mostly
zooplankton Zooplankton (, ) are heterotrophic (sometimes detritivorous) plankton (cf. phytoplankton). Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word ''zooplankton'' is derived from the Greek ''zoon'' (), meaning "animal ...

and
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular microa ...
, are buried underneath
sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles to ...
and subjected to both intense heat and pressure. Petroleum has mostly been recovered by
oil drilling , such as this one located south of Midland, Texas, is a common sight in West Texas An oil well is a boring (earth), boring in the Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as as ...
. Drilling is carried out after studies of structural geology, sedimentary basin analysis, and reservoir characterisation. Recent improvements to technologies have also led to exploitation of other unconventional reserves such as
oil sands Tar sandstone from United_States.html"_style="text-decoration:_none;"class="mw-redirect"_title="California,_United_States">California,_United_States_ Oil_sands,_tar_sands,_crude_bitumen,_or_bituminous_sands,_are_a_type_of_unconventional ...
and
oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced, called shale oil. Shale oil is a substitute for conventional crude oi ...
. Once extracted, oil is refined and separated, most easily by
distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. Dry distillation is the heating of solid materials to produce gaseous products ...
, into numerous products for direct use or use in manufacturing, such as
gasoline Gasoline () or petrol () (see the etymology for naming differences) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines. It consists mostly of organic compoun ...
(petrol), diesel and
kerosene Kerosene, also known as paraffin, is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning "wax", and was regis ...
to
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asph ...
and chemical
reagent 200px, Reactants, such as sulfur (''pictured''), are the starting materials that are used in chemical reactions. A reagent is a substance or compound added to a system to cause a chemical reaction, or added to test if a reaction occurs. The terms ...
s used to make
plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptability, ...
s,
pesticide Pesticides are substances that are meant to control pests. The term pesticide includes all of the following: herbicide, insecticides (which may include insect growth regulators, termiticides, etc.) nematicide, molluscicide, piscicide, avicide, ...
s and
pharmaceuticals A medication (also referred to as medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and relies on ...
. Petroleum is used in manufacturing a wide variety of materials, and it is estimated that the world consumes about 100 million
barrels A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wood or metal hoops. The word vat is often used for large containers for liquids, usual ...
each day. Petroleum production can be extremely profitable and was important for economic development in the 20th century, with some countries, so called "
oil states A petrostate is a nation whose economy is heavily dependent on the extraction and export of oil or natural gas. The presence alone of large oil and gas industries does not define a petrostate, as countries like Norway, Canada, and the United States ...
", gaining significant economic and international power because of their control of oil production. Petroleum exploitation has significant negative environmental and social consequences. Most significantly, extraction,
refining{{Unreferenced, date=December 2009 Refining (also perhaps called by the mathematical term affining) is the process of purification of a (1) substance or a (2) form. The term is usually used of a natural resource that is almost in a usable form, but wh ...
and
burning Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...
of petroleum fuels all release large quantities of
greenhouse gas A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxid ...
es, so petroleum is one of the major contributors to climate change. At the same time, parts of the petroleum industry actively suppressed science and policy that aimed to prevent the
climate crisis Climate crisis is a term describing global warming and climate change, and their consequences. The term has been used to describe the threat of global warming to the planet, and to urge aggressive climate change mitigation. For example, a Janua ...
. Other negative environmental effects include the environmental impacts of exploration and exploitation of petroleum reserves, such as
oil spill An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into the ...
s, and air and water pollution at the sites of utilization. All of these environmental impacts have direct health consequences for humans. Additionally, oil has also been a source of conflict leading to both and other kinds of conflicts (for example, oil revenue funded the
Islamic State of Iraq and the Levant {{Infobox war faction , name = Islamic State of Iraq and the Levant , native_name = {{rtl-lang, ar, الدولة الإسلامية في العراق والشام''{{transl, ar, ad-Dawlah al-Islāmiyah fī 'l-ʿIrāq wa-sh-Shām'' , war = the Iraq ...
). Production of petroleum is expected to reach
peak oil''For Peak brand motor oil, see Peak (automotive products).'' Hubbert's upper-bound prediction for US crude oil production (1956) in red, and actual lower-48 states production through to 2014 in green Peak oil is the year when the maximum rate ...
before 2040 as global economies reduce dependencies on petroleum as part of
climate change mitigation Climate change mitigation consists of actions to limit global warming and its related effects. This involves reductions in human emissions of greenhouse gases (GHGs) as well as activities that reduce their concentrations in the atmosphere. Fossil ...
and a transition towards
renewable energy Renewable energy is useful energy that is collected from renewable resources, which are naturally replenished on a human timescale, including carbon neutral sources like sunlight, wind, rain, tides, waves, and geothermal heat. The term often a ...
and
electrification Electrification is the process of powering by electricity and, in many contexts, the introduction of such power by changing over from an earlier power source. The broad meaning of the term, such as in the history of technology, economic history, a ...

. This is expected to have significant economic impacts that stakeholders argue need to be anticipated by a
just transition Just Transition is a framework developed by the trade union movement to encompass a range of social interventions needed to secure workers' rights and livelihoods when economies are shifting to sustainable production, primarily combating climate ch ...
stranded assetStranded assets are "assets that have suffered from unanticipated or premature write-downs, devaluations or conversion to liabilities". Stranded assets can be caused by a variety of factors and are a phenomenon inherent in the 'creative destruction' ...
s of the petroleum industry.

# Etymology

The word ''petroleum'' comes from
Medieval Latin Medieval Latin was the form of Latin used in Roman Catholic Western Europe during the Middle Ages. In this region it served as the primary written language, though local languages were also written to varying degrees. Latin functioned as the mai ...
(literally "rock oil"), which comes from
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became the dominant language ...
''
petra Petra ( ar, ٱلْبَتْرَاء, Al-Batrāʾ; grc, Πέτρα, "Rock"), originally known to its inhabitants in as Raqmu or Raqēmō (𐢚𐢛𐢓𐢈), is a historic and archaeological city in southern Jordan. Petra lies around Jabal Al-Madbah in ...
'', "rock", (from grc, πέτρα, translit=petra, "rock") and Latin ''
oleum Oleum (Latin ''oleum'', meaning oil), or fuming sulfuric acid, is a term referring to solutions of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid (also known as pyrosulfuric acid). Oleum ...
'', "oil", (from grc, ἔλαιον, translit=élaion, "oil"). The term was used in the treatise ''
De Natura Fossilium ''De Natura Fossilium'' is a scientific text written by Georg Bauer also known as Georgius Agricola, first published in 1546. The book represents the first scientific attempt to categorize minerals, rocks and sediments since the publication of Pli ...
'', published in 1546 by the German mineralogist Georg Bauer, also known as Georgius Agricola. In the 19th century, the term ''petroleum'' was often used to refer to
mineral oil Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils. The name ''mineral oil'' by itself is imprecise, ...
s produced by distillation from mined organic solids such as
cannel coal Cannel coal or candle coal is a type of bituminous coal, also classified as terrestrial type oil shale.Hutton(1987)Dyni (2006), pp. 3–4Speight (2012), pp. 6–7 Due to its physical morphology and low mineral content cannel coal is considered to ...
(and later
oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced, called shale oil. Shale oil is a substitute for conventional crude oi ...
) and refined oils produced from them; in the United Kingdom, storage (and later transport) of these oils were regulated by a series of Petroleum Acts, from the ''Petroleum Act 1863'' onwards.

# History

## Early

Petroleum, in one form or another, has been used since ancient times, and is now important across society, including in economy, politics and technology. The rise in importance was due to the invention of the
internal combustion engine An internal combustion engine (ICE) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, t ...
, the rise in
commercial aviation Commercial aviation is the part of civil aviation (both general aviation and scheduled airline services) that involves operating aircraft for hire to transport passengers or multiple loads of cargo. History Origins Harry Bruno and Juan Trippe w ...
, and the importance of petroleum to industrial organic chemistry, particularly the synthesis of plastics, fertilisers, solvents, adhesives and pesticides. More than 4000 years ago, according to
Herodotus Herodotus (; grc, Ἡρόδοτος, ''Hēródotos'', ; BC) was an ancient Greek historian who was born in Halicarnassus in the Persian Empire (modern-day Bodrum, Turkey). He is known for having written the book ''The Histories'' ( grc, Ἱσ ...
and
Diodorus Siculus Diodorus Siculus (; grc-koi, Διόδωρος Σικελιώτης ''Diodoros Sikeliotes'';  1st century BC) or Diodorus of Sicily was an ancient Greek historian. He is known for writing the monumental universal history ''Bibliotheca histori ...
,
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asph ...
was used in the construction of the walls and towers of
Babylon ''Bābili(m)'' * sux, 𒆍𒀭𒊏𒆠 * arc, 𐡁𐡁𐡋 ''Babil'' * grc-gre, Βαβυλών ''Babylṓn'' * he, בָּבֶל ''Bavel'' * peo, 𐎲𐎠𐎲𐎡𐎽𐎢 ''Bābiru'' * elx, 𒀸𒁀𒉿𒇷 ''Babili'' *Kassite: ''Karanduniash'' , image ...
; there were oil pits near Ardericca (near Babylon), and a pitch spring on
Zacynthus Zakynthos (also spelled Zakinthos; el, Ζάκυνθος, Zákynthos ; it, Zacinto ) or Zante (, , ; el, Τζάντε, Tzánte ; from the Venetian form) is a Greek island in the Ionian Sea. It is the third largest of the Ionian Islands. Zakynthos i ...
. Great quantities of it were found on the banks of the river
Issus Issus may refer to: * Issus (Cilicia), an ancient settlement in the modern Turkish province of Hatay ** Battle of Issus, in 333 BC, in which Alexander the Great defeated Darius III * Issus (river), a river near the town and battle site * Issus (dio ...
, one of the tributaries of the
Euphrates The Euphrates () is the longest and one of the most historically important rivers of Western Asia. Together with the Tigris, it is one of the two defining rivers of Mesopotamia (the "Land Between the Rivers"). Originating in the Armenian Highlan ...
. Ancient tablets indicate the medicinal and lighting uses of petroleum in the upper levels of their society. The use of petroleum in ancient China dates back to more than 2000 years ago. In
I Ching The ''I Ching'' or ''Yi Jing'' (, ), usually translated as ''Book of Changes'' or ''Classic of Changes'', is an ancient Chinese divination text and among the oldest of the Chinese classics. Originally a divination manual in the Western Zhou p ...
, one of the earliest Chinese writings cites that oil in its raw state, without refining, was first discovered, extracted, and used in China in the first century BCE. In addition, the Chinese were the first to record the use of petroleum as fuel as early as the fourth century BCE. By 347 CE, oil was produced from bamboo-drilled wells in China.
Crude oil Petroleum (), also known as crude oil and oil, is a naturally occurring, yellowish-black liquid found in geological formations beneath the Earth's surface. It is commonly refined into various types of fuels. Components of petroleum are separate ...
was often distilled by Persian chemists, with clear descriptions given in Arabic handbooks such as those of
Muhammad ibn Zakarīya Rāzi Abū Bakr Muhammad Zakariyyā Rāzī ( fa, ابوبكر محمّد زکرياى رازى ''Abūbakr Mohammad-e Zakariyā-ye Rāzī'', also known by his Latinized name Rhazes () or Rasis; 854–925 CE), was a Persian polymath, physician, alchemist, ...
(Rhazes). The streets of
Baghdad Baghdad (; ar, بَغْدَاد ) is the capital of Iraq and one of the largest cities in the Arab world, and compared to its large population it has a small area at just 673 square kilometers (260 sq mi). Located along the Tigris, near the ru ...

were paved with tar, derived from petroleum that became accessible from natural fields in the region. In the 9th century,
oil field A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. Petroleum reservoirs are broadly classified as ''conventional'' and ''unconventional'' reservoirs. In conventiona ...

s were exploited in the area around modern
Baku Baku (, ; az, Bakı, ) is the capital and largest city of Azerbaijan, as well as the largest city on the Caspian Sea and of the Caucasus region. Baku is located below sea level, which makes it the lowest lying national capital in the world and a ...
,
Azerbaijan Azerbaijan (, ; az, Azərbaycan ), officially the Republic of Azerbaijan ( az, Azərbaycan Respublikası ), is a country in the Caucasus region of Eurasia. Located at the crossroads of Eastern Europe and Western Asia, it is bounded by the Caspia ...
. These fields were described by the
Arab geographer The Arabs (singular Arab ; singular ar, عَرَبِيٌّ, ISO 233: , Arabic pronunciation: , plural ar, عَرَبٌ, ISO 233: , Arabic pronunciation: ) are an ethnic group mainly inhabiting the Arab world. In modern usage the term refers to th ...
Abu al-Hasan 'Alī al-Mas'ūdī Al-Mas'udi ( ar, أَبُو ٱلْحَسَن عَلِيّ ٱبْن ٱلْحُسَيْن ٱبْن عَلِيّ ٱلْمَسْعُودِيّ, '; –956) was an Arab historian, geographer and traveler. He is sometimes referred to as the "Herodotus of ...
in the 10th century, and by
Marco Polo Marco Polo (; ; ; September 15, 1254January 8, 1324) was a Venetian merchant, explorer, and writer who travelled through Asia along the Silk Road between 1271 and 1295. His travels are recorded in ''The Travels of Marco Polo'' (also known as ...
in the 13th century, who described the output of those wells as hundreds of shiploads. Arab and Persian chemists also distilled crude oil in order to produce
flammable , Germany Image:Tu braunschweig 750 grad ofen.jpg, 250px, Germany, German test apparatus for determining combustibility at Technische Universität Braunschweig A combustible material is something that can combust (burn) in air. Flammable mater ...
products for military purposes. Through
Islamic Spain#REDIRECT Al-Andalus {{Redirect category shell, 1= {{R from other capitalisation ...
, distillation became available in
Western Europe Western Europe is the region of Europe farthest from Asia, with the countries and territories included varying depending on context. After the beginning of foreign exploration in the Age of Discovery, roughly from the 15th century, the concept ...
by the 12th century. It has also been present in Romania since the 13th century, being recorded as păcură. Sophisticated oil pits, 15 to 20 feet deep, were dug by the
Seneca People The Seneca () (Seneca: ''Onödowáʼga'':, "Great Hill People") are a group of Indigenous Iroquoian-speaking people native to who historically lived south of Lake Ontario, one of the five Great Lakes in North America. Their nation was the farthest ...
and other
Iroqouis The Iroquois ( or ) or Haudenosaunee (; "People of the Longhouse") are an indigenous confederacy in northeast North America. They were known during the colonial years to the French as the Iroquois League, later as the Iroquois Confederacy and t ...
in
Western Pennsylvania Western Pennsylvania is a region in the U.S. state of Pennsylvania, covering the western third of the state. Pittsburgh is the region's principal city, with a metropolitan area population of about 2.4 million people, and serves as its economic an ...
as early as 1415-1450. The French General
Louis-Joseph de Montcalm Louis-Joseph de Montcalm-Grozon, marquis de Montcalm de Saint-Veran (28 February 1712 – 14 September 1759) was a French soldier best known as the commander of the forces in North America during the Seven Years' War (whose North American thea ...
encountered Seneca using petroleum for ceremonial fires and as a healing lotion during a visit to Fort Duquesne in 1750. Early British explorers to
Myanmar Myanmar (; my, မြန်မာ ) or Burma ( my, ဗမာ ), officially the Republic of the Union of Myanmar, is a country in Southeast Asia. Myanmar is bordered by Bangladesh and India to its northwest, China to its northeast, Laos and ...
documented a flourishing oil extraction industry based in
Yenangyaung Yenangyaung ( my, ရေနံချောင်း; literally "stream of oil") is a city in the Magway Region of central Myanmar, located on the Irrawaddy River and 363 miles from Yangon. Until 1974, it remained the capital city of both Minbu Divis ...
that, in 1795, had hundreds of hand-dug wells under production.
Pechelbronn Merkwiller-Pechelbronn () is a commune in the Bas-Rhin department in Grand Est in north-eastern France. It is notable as the original home of oil sands mining. Oil sands were mined from 1745 in Merkwiller-Pechelbronn, initially under the directio ...
(Pitch fountain) is said to be the first European site where petroleum has been explored and used. The still active Erdpechquelle, a spring where petroleum appears mixed with water has been used since 1498, notably for medical purposes. Oil sands have been mined since the 18th century. In
Wietze Wietze is a municipality in the district of Celle, in Lower Saxony, Germany. It is situated at the confluence of the river Aller and its tributary Wietze, approx. 15 km west of Celle. It is the site of the German Oil Museum. References ...
in lower Saxony, natural asphalt/bitumen has been explored since the 18th century. Both in Pechelbronn as in Wietze, the coal industry dominated the petroleum technologies.

## Modern

Chemist James Young noticed a natural petroleum seepage in the
Riddings Riddings is a large village in Derbyshire, England. The appropriate ward of the Amber Valley Council is called Ironville and Riddings. The population of this ward as at the 2011 census was 5,821. It is located south of Alfreton near the hamlet of ...
colliery Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ...
at
Alfreton Alfreton ( ) is a town and civil parish in the Amber Valley district of Derbyshire, England. The town was formerly a Norman Manor and later an Urban District. The population of the Alfreton parish was 7,971 at the 2011 Census. The villages of Ir ...
,
Derbyshire Derbyshire () is a county in the East Midlands of England. Much of the Peak District National Park lies within Derbyshire, containing the southern extremity of the Pennine range of hills, which extend into the north of the county. It contains pa ...
from which he distilled a light thin oil suitable for use as lamp oil, at the same time obtaining a more viscous oil suitable for lubricating machinery. In 1848, Young set up a small business refining the crude oil. Young eventually succeeded, by distilling
cannel coal Cannel coal or candle coal is a type of bituminous coal, also classified as terrestrial type oil shale.Hutton(1987)Dyni (2006), pp. 3–4Speight (2012), pp. 6–7 Due to its physical morphology and low mineral content cannel coal is considered to ...
at a low heat, in creating a fluid resembling petroleum, which when treated in the same way as the seep oil gave similar products. Young found that by slow distillation he could obtain a number of useful liquids from it, one of which he named "paraffine oil" because at low temperatures it congealed into a substance resembling paraffin wax. The production of these oils and solid
paraffin wax Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal or oil shale that consists of a mixture of hydrocarbon molecules containing between twenty and forty carbon atoms. It is solid at room temperature and begins ...
from coal formed the subject of his patent dated 17 October 1850. In 1850 Young & Meldrum and Edward William Binney entered into partnership under the title of E.W. Binney & Co. at
Bathgate Bathgate ( sco, Bathket or , gd, Both Chèit) is a town in West Lothian, Scotland, west of Livingston and adjacent to the M8 motorway. Nearby towns are Armadale, Blackburn, Linlithgow, Livingston, West Calder and Whitburn. Situated south of th ...
in
West Lothian West Lothian ( sco, Wast Lowden; gd, Lodainn an Iar) is one of the 32 council areas of Scotland, and one of its historic counties. The county, which was historically known as Linlithgowshire, was bounded geographically by the Avon to the west and ...
and E. Meldrum & Co. at Glasgow; their works at Bathgate were completed in 1851 and became the first truly commercial oil-works in the world with the first modern oil refinery. The world's first oil refinery was built in 1856 by
Ignacy Łukasiewicz Jan Józef Ignacy Łukasiewicz (; 8 March 1822 – 7 January 1882) was a Polish pharmacist, engineer, businessman, inventor, and philanthropist. He was one of the most prominent philanthropists in the Kingdom of Galicia and Lodomeria, crown land of ...
. His achievements also included the discovery of how to distill kerosene from seep oil, the invention of the modern kerosene lamp (1853), the introduction of the first modern street lamp in Europe (1853), and the construction of the world's first modern oil well (1854). The demand for petroleum as a fuel for lighting in North America and around the world quickly grew.
Edwin Drake Edwin Laurentine Drake (March 29, 1819 – November 9, 1880), also known as Colonel Drake, was an American businessman and the first American to successfully drill for oil. Early life Edwin Drake was born in Greenville, Greene County, New Yo ...
's 1859 well near Titusville, Pennsylvania, is popularly considered the first modern well. Already 1858 Georg Christian Konrad Hunäus had found a significant amount of petroleum while drilling for
lignite Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It is considered the lowest rank of coal due to its relatively low heat content. It has a carbon content around 25 to ...
1858 in
Wietze Wietze is a municipality in the district of Celle, in Lower Saxony, Germany. It is situated at the confluence of the river Aller and its tributary Wietze, approx. 15 km west of Celle. It is the site of the German Oil Museum. References ...
, Germany. Wietze later provided about 80% of the German consumption in the Wilhelminian Era. The production stopped in 1963, but Wietze has hosted a Petroleum Museum since 1970. Drake's well is probably singled out because it was drilled, not dug; because it used a steam engine; because there was a company associated with it; and because it touched off a major boom. However, there was considerable activity before Drake in various parts of the world in the mid-19th century. A group directed by Major Alexeyev of the Bakinskii Corps of Mining Engineers hand-drilled a well in the Baku region of Bibi-Heybat in 1846. There were engine-drilled wells in West Virginia in the same year as Drake's well. An early commercial well was hand dug in
Poland Poland ( pl, Polska ), officially the Republic of Poland ( pl, Rzeczpospolita Polska, links=no ), is a country located in Central Europe. It is divided into 16 administrative provinces, covering an area of , and has a largely temperate seaso ...
in 1853, and another in nearby
Romania Romania ( ; ro, România ) is a country located at the crossroads of Central, Eastern, and Southeastern Europe. It shares land borders with Bulgaria to the south, Ukraine to the north, Hungary to the west, Serbia to the southwest, and Moldov ...
in 1857. At around the same time the world's first, small, oil refinery was opened at
Jasło Jasło is a county town in south-eastern Poland with 36,641 inhabitants, as of 31 December 2012. It is situated in the Subcarpathian Voivodeship (since 1999), and it was previously part of Krosno Voivodeship (1975–1998). It is located in Lesser ...
in Poland, with a larger one opened at
Ploiești Ploiești (, , ), formerly spelled Ploești, is a city and county seat in Prahova County, Romania. Part of the historical region of Muntenia, it is located north of Bucharest. The area of the city is around . It borders the Blejoi commune in the ...
in Romania shortly after. Romania is the first country in the world to have had its annual crude oil output officially recorded in international statistics: 275 tonnes for 1857. The first commercial oil well in Canada became operational in 1858 at
Oil Springs, Ontario Oil Springs is a village in Lambton County, Ontario, Canada, located along Former Provincial Highway 21 south of Oil City. The village, an enclave within Enniskillen Township, is the site of North America's first commercial oil well. It is home to ...
(then
Canada West The Province of Canada (or the United Province of Canada or the United Canadas) was a British colony in North America from 1841 to 1867. Its formation reflected recommendations made by John Lambton, 1st Earl of Durham, in the Report on the Af ...
).Oil Museum of Canada, Black Gold: Canada's Oil Heritage, Oil Springs: Boom & Bust
James Miller Williams James Miller Williams (September 14, 1818 – November 25, 1890) was a Canadian-American businessman and politician. Williams is best known for establishing the first commercially successful oil well in 1858 and igniting the first oil boom in N ...
dug several wells between 1855 and 1858 before discovering a rich reserve of oil four metres below ground. Williams extracted 1.5 million litres of crude oil by 1860, refining much of it into kerosene lamp oil. Williams's well became commercially viable a year before Drake's Pennsylvania operation and could be argued to be the first commercial oil well in North America. The discovery at Oil Springs touched off an
oil boom An oil boom is a period of large inflow of income as a result of high global oil prices or large oil production in an economy. Generally, this short period initially brings economic benefits, in terms of increased GDP growth, but might later lead t ...
which brought hundreds of speculators and workers to the area. Advances in drilling continued into 1862 when local driller Shaw reached a depth of 62 metres using the spring-pole drilling method. On January 16, 1862, after an explosion of
natural gas Natural gas (also called fossil gas; sometimes just gas) is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carb ...
Canada's first oil gusher came into production, shooting into the air at a recorded rate of 3,000 barrels per day. By the end of the 19th century the Russian Empire, particularly the
Branobel The Petroleum Production Company Nobel Brothers, Limited, or Branobel (short for братьев Нобель "brat'yev Nobel" — "Nobel Brothers" in Russian), was an oil company set up by Ludvig Nobel and Baron Peter von Bilderling. It operated ma ...
company in
Azerbaijan Azerbaijan (, ; az, Azərbaycan ), officially the Republic of Azerbaijan ( az, Azərbaycan Respublikası ), is a country in the Caucasus region of Eurasia. Located at the crossroads of Eastern Europe and Western Asia, it is bounded by the Caspia ...
, had taken the lead in production.Akiner(2004), p. 5 Access to oil was and still is a major factor in several military conflicts of the twentieth century, including
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a global war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all the great powers—forming two opposing milit ...
, during which oil facilities were a major strategic asset and were extensively bombed. The
German invasion of the Soviet Union#REDIRECT Operation Barbarossa {{R from other capitalisation ...
included the goal to capture the Baku oilfields, as it would provide much needed oil-supplies for the German military which was suffering from blockades. Oil exploration in North America during the early 20th century later led to the US becoming the leading producer by mid-century. As petroleum production in the US peaked during the 1960s, however, the United States was surpassed by Saudi Arabia and the Soviet Union. In 1973, Saudi Arabia and other
Arab nations The Arab world ( ar, العالم العربي '), formally the Arab homeland ( '), also known as the Arab nation ( '), the Arabsphere, or the Arab states, consists of the 22 Arab countries which are members of the Arab League. A majority of thes ...
imposed an
oil embargoAn oil embargo is an economic situation wherein entities engage in an embargo to limit the transport of petroleum to or from an area, in order to exact some desired outcome. One commentator states, " oil embargo is not a common commercial practice; i ...
against the United States, United Kingdom, Japan and other Western nations which supported
Israel Israel (; he, יִשְׂרָאֵל; ar, إِسْرَائِيل), officially known as the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, '), is a country in Western Asia, located on the southeastern shore of the Mediterranean Se ...
in the
Yom Kippur War#redirectYom Kippur War#redirectYom Kippur War {{R from other capitalisation ...
{{R from other capitalisation ...
of October 1973. The embargo caused an oil crisis with many short- and long-term effects on global politics and the global economy. Today, about 90 percent of vehicular fuel needs are met by oil. Petroleum also makes up 40 percent of total energy consumption in the United States, but is responsible for only 1 percent of electricity generation. Petroleum's worth as a portable, dense energy source powering the vast majority of vehicles and as the base of many industrial chemicals makes it one of the world's most important
commodities In economics, a commodity is an economic good, usually a resource, that has full or substantial fungibility: that is, the market treats instances of the good as equivalent or nearly so with no regard to who produced them. The price of a commodit ...
. The top three oil producing countries are
Russia Russia (russian: link=no, Россия, , ), or the Russian Federation, is a country spanning Eastern Europe and Northern Asia. It is the largest country in the world, covering and encompassing more than one-eighth of the Earth's inhabited l ...
,
Saudi Arabia (Shahada) , national_anthem = "" "National Anthem of Saudi Arabia" , image_map = Saudi Arabia (orthographic projection).svg , capital = Riyadh , coordinates = , largest_city = Riyadh , official_languages = Arabic , languages_type = Spoken l ...
and the
United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major self-governing territories, 326 India ...
. In 2018, due in part to developments in
hydraulic fracturing#REDIRECT Hydraulic fracturing {{R from other capitalisation ...
and
horizontal drilling Directional drilling (or slant drilling) is the practice of drilling non-vertical bores. It can be broken down into four main groups: oilfield directional drilling, utility installation directional drilling (horizontal directional drilling), dire ...
, the United States became the world's largest producer. About 80 percent of the world's readily accessible reserves are located in the Middle East, with 62.5 percent coming from the Arab 5:
Saudi Arabia (Shahada) , national_anthem = "" "National Anthem of Saudi Arabia" , image_map = Saudi Arabia (orthographic projection).svg , capital = Riyadh , coordinates = , largest_city = Riyadh , official_languages = Arabic , languages_type = Spoken l ...
,
United Arab Emirates The United Arab Emirates (UAE; Arabic: الإمارات العربية المتحدة '), sometimes simply called the Emirates (Arabic: الإمارات '), is a country in Western Asia located at the eastern end of the Arabian Peninsula. It b ...
,
Iraq Iraq ( ar, ٱلْعِرَاق, '; ku, عێراق '), officially the Republic of Iraq ( ar, جُمْهُورِيَّة ٱلْعِرَاق '; ku, کۆماری عێراق '), is a country in Western Asia, bordered by Turkey to the north, Iran to th ...
,
Qatar Qatar (, , or ; ar, قطر ' ; local vernacular pronunciation: ), officially the State of Qatar ( ar, دولة قطر '), is a country located in Western Asia, occupying the small Qatar Peninsula on the northeastern coast of the Arabian Peni ...
and
Kuwait Kuwait (; ar, الكويت ', or ), officially the State of Kuwait ( ar, دولة الكويت '), is a country in Western Asia. It is situated in the northern edge of Eastern Arabia at the tip of the Persian Gulf, bordering Iraq to the north ...
. A large portion of the world's total oil exists as unconventional sources, such as
bitumen Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asph ...

in
Athabasca oil sands#REDIRECT Athabasca oil sands#REDIRECT Athabasca oil sands {{R from other capitalisation ...
{{R from other capitalisation ...

and
extra heavy oilHeavy crude oil (or extra heavy crude oil) is highly-viscous oil that cannot easily flow to production wells under normal reservoir conditions. It is referred to as "heavy" because its density or specific gravity is higher than that of light crude o ...
in the
Orinoco Belt The Orinoco Belt is a territory in the southern strip of the eastern Orinoco River Basin in Venezuela which overlies the world's largest deposits of petroleum. Its local Spanish name is ''Faja Petrolífera del Orinoco'' (Orinoco Petroleum Belt). Th ...
. While significant volumes of oil are extracted from oil sands, particularly in Canada, logistical and technical hurdles remain, as oil extraction requires large amounts of heat and water, making its net energy content quite low relative to conventional crude oil. Thus, Canada's oil sands are not expected to provide more than a few million barrels per day in the foreseeable future.

# Composition

Petroleum includes not only crude oil, but all liquid, gaseous and solid
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarb ...
s. Under surface pressure and temperature conditions, lighter hydrocarbons
methane Methane ( or ) is a chemical compound with the chemical formula (one atom of carbon and four atoms of hydrogen). It is a group-14 hydride and the simplest alkane, and is the main constituent of natural gas. The relative abundance of methane on ...
,
ethane Ethane ( or ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroche ...
,
propane Propane () is a three-carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a ...
and
butane Butane () or ''n''-butane is an alkane with the formula C4H10. Butane is a gas at room temperature and atmospheric pressure. Butane is a highly flammable, colorless, easily liquefied gas that quickly vaporizes at room temperature. The name butane ...
exist as gases, while
pentane Pentane is an organic compound with the formula C5H12—that is, an alkane with five carbon atoms. The term may refer to any of three structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, pentane means exclusively the ''n ...
and heavier hydrocarbons are in the form of liquids or solids. However, in an underground
oil reservoir A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. Petroleum reservoirs are broadly classified as ''conventional'' and ''unconventional'' reservoirs. In conventiona ...
the proportions of gas, liquid, and solid depend on subsurface conditions and on the
phase diagram#REDIRECT Phase diagram#REDIRECT Phase diagram {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
of the petroleum mixture. An
oil well , such as this one located south of Midland, Texas, is a common sight in West Texas An oil well is a boring (earth), boring in the Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as as ...

produces predominantly crude oil, with some natural gas dissolved in it. Because the pressure is lower at the surface than underground, some of the gas will come out of
solution Making a NaCl)_in_water.html" style="text-decoration: none;"class="mw-redirect" title="Salt">table salt (sodium chloride">NaCl) in water">Salt">table salt (sodium chloride">NaCl) in water. The salt is the solute and the water the solve ...
and be recovered (or burned) as ''associated gas'' or ''solution gas''. A
gas well , such as this one located south of Midland, Texas, is a common sight in West Texas An oil well is a boring (earth), boring in the Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as as ...
produces predominantly
natural gas Natural gas (also called fossil gas; sometimes just gas) is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carb ...
. However, because the underground temperature is higher than at the surface, the gas may contain heavier hydrocarbons such as pentane,
hexane Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. Hexane is a significant constituent of gasoline. It is a colorless liquid, odorless when pure, and with boiling points approxim ...
, and
heptane Heptane or ''n''-heptane is the straight-chain alkane with the chemical formula H3C(CH2)5CH3 or C7H16, and is one of the main components of gasoline (petrol). When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the ...
in the
gaseous state Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or compo ...
. At surface conditions these will
condense Condensation is the change of the physical state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water ...
out of the gas to form "
natural gas condensate Natural-gas condensate, also called natural gas liquids, is a low-density mixture of hydrocarbon liquids that are present as gaseous components in the raw natural gas produced from many natural gas fields. Some gas species within the raw natural g ...
", often shortened to ''condensate.'' Condensate resembles gasoline in appearance and is similar in composition to some volatile
light crude oilLight crude oil is liquid petroleum that has a low density and flows freely at room temperature. It has a low viscosity, low specific gravity and high API gravity due to the presence of a high proportion of light hydrocarbon fractions. It generally h ...
s. The proportion of light hydrocarbons in the petroleum mixture varies greatly among different
oil fields A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. Petroleum reservoirs are broadly classified as ''conventional'' and ''unconventional'' reservoirs. In conventiona ...
, ranging from as much as 97 percent by weight in the lighter oils to as little as 50 percent in the heavier oils and
bitumen Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asph ...

s. The hydrocarbons in crude oil are mostly
alkane , the simplest alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree st ...
s,
cycloalkane In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing a ...
s and various
aromatic hydrocarbon Aromatic compounds are those chemical compounds (most commonly organic) that contain one or more rings with pi electrons delocalized all the way around them. In contrast to compounds that exhibit aromaticity, aliphatic compounds lack this delocali ...
s, while the other organic compounds contain
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about t ...
,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well a ...
and
sulfur Sulfur (in traditional lay Commonwealth English: sulphur) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecul ...
, and trace amounts of metals such as iron, nickel, copper and
vanadium Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer (passiv ...
. Many oil reservoirs contain live bacteria. The exact molecular composition of crude oil varies widely from formation to formation but the proportion of
chemical element 400px, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same numbers of protons in their atomic nuclei. Unlike chemical compounds, chemical elements cannot be br ...
s varies over fairly narrow limits as follows: Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of each varies from oil to oil, determining the properties of each oil. Crude oil varies greatly in appearance depending on its composition. It is usually black or dark brown (although it may be yellowish, reddish, or even greenish). In the reservoir it is usually found in association with natural gas, which being lighter forms a "gas cap" over the petroleum, and
saline water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). The salt concentration is usually expressed in parts per thousand (permille, ‰) or parts per million (ppm) ...
which, being heavier than most forms of crude oil, generally sinks beneath it. Crude oil may also be found in a semi-solid form mixed with sand and water, as in the
Athabasca oil sands#REDIRECT Athabasca oil sands#REDIRECT Athabasca oil sands {{R from other capitalisation ...
{{R from other capitalisation ...

in Canada, where it is usually referred to as crude
bitumen Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asph ...

. In Canada, bitumen is considered a sticky, black, tar-like form of crude oil which is so thick and heavy that it must be heated or diluted before it will flow. Venezuela also has large amounts of oil in the
Orinoco oil sands The Orinoco Belt is a territory in the southern strip of the eastern Orinoco River Basin in Venezuela which overlies the world's largest deposits of petroleum. Its local Spanish name is ''Faja Petrolífera del Orinoco'' (Orinoco Petroleum Belt). Th ...
, although the hydrocarbons trapped in them are more fluid than in Canada and are usually called
extra heavy oilHeavy crude oil (or extra heavy crude oil) is highly-viscous oil that cannot easily flow to production wells under normal reservoir conditions. It is referred to as "heavy" because its density or specific gravity is higher than that of light crude o ...
. These oil sands resources are called
unconventional oilUnconventional oil is petroleum produced or extracted using techniques other than the conventional method (oil well). Industry and governments across the globe are investing in unconventional oil sources due to the increasing scarcity of conventional ...
to distinguish them from oil which can be extracted using traditional oil well methods. Between them, Canada and
Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in the Ca ...
contain an estimated of bitumen and extra-heavy oil, about twice the volume of the world's reserves of conventional oil. Petroleum is used mostly, by volume, for refining into
fuel oil Fuel oil (also known as heavy oil, marine fuel, bunker, furnace oil, or gasoil) is a fraction obtained from petroleum distillation. It includes distillates - the lighter fractions, and residues - the heavier fractions. The term ''fuel oil'' genera ...
and gasoline, both important ''"
primary energy Primary energy (PE) is an energy form found in nature that has not been subjected to any human engineered conversion process. It is energy contained in raw fuels, and other forms of energy received as input to a system. Primary energy can be non ...
"'' sources. 84 percent by volume of the hydrocarbons present in petroleum is converted into energy-rich fuels (petroleum-based fuels), including gasoline, diesel, jet, heating, and other fuel oils, and
liquefied petroleum gas Tank cars in a Canadian train for carrying liquefied petroleum gas by rail. Liquefied petroleum gas (LPG or LP gas), is a flammable mixture of hydrocarbon gases with a mixture of 48% propane, 50% butane, and 2% pentane. LPG is used as fuel ga ...
. The lighter grades of crude oil produce the best yields of these products, but as the world's reserves of light and medium oil are depleted,
oil refineries An oil refinery or petroleum refinery is an industrial process plant where crude oil is transformed and refined into useful products such as petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, je ...
are increasingly having to process heavy oil and bitumen, and use more complex and expensive methods to produce the products required. Because heavier crude oils have too much carbon and not enough hydrogen, these processes generally involve removing carbon from or adding hydrogen to the molecules, and using
fluid catalytic cracking Fluid catalytic cracking (FCC) is one of the most important conversion processes used in petroleum refineries. It is widely used to convert the high-boiling point, high-molecular weight hydrocarbon fractions of petroleum crude oils into more valuabl ...
to convert the longer, more complex molecules in the oil to the shorter, simpler ones in the fuels. Due to its high
energy density In physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It may also be used for energy per unit mass, though a more accurate term for this is specific energy (or gravimetric energy density). ...

, easy transportability and , oil has become the world's most important source of energy since the mid-1950s. Petroleum is also the raw material for many
chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., witho ...
products, including
pharmaceutical A medication (also referred to as medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and relies on ...
s,
solvent A solvent (from the Latin ''solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for polar mo ...
s,
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from li ...
s,
pesticide Pesticides are substances that are meant to control pests. The term pesticide includes all of the following: herbicide, insecticides (which may include insect growth regulators, termiticides, etc.) nematicide, molluscicide, piscicide, avicide, ...
s, and plastics; the 16 percent not used for energy production is converted into these other materials. Petroleum is found in
porousPorosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure the ...
rock formations , Nevada, USA File:Hajdučka Vrata.JPG">"Hajdučka vrata" on rock outcrop. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term ''rock Geological formation, formation'' can also refer t ...
in the upper
strata (Argentina). , Canada. These are Middle Cambrian marine sediments. This formation covers over half of Nova Scotia and is recorded as being 8,800 m (29,000 ft) thick in some areas. In geology and related fields, a stratum (plural: strata) is a l ...
of some areas of the
Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper ...
. There is also petroleum in oil sands (tar sands). Known
oil reserves Oil reserves denote the amount of crude oil that can be technically recovered at a cost that is financially feasible at the present price of oil. Hence reserves will change with the price, unlike oil resources, which include all oil that can be te ...

are typically estimated at around 190 km3 (1.2
trillion A trillion is a number with two distinct definitions: *1,000,000,000,000, i.e. one million million, or (ten to the twelfth power), as defined on the short scale. This is now the meaning in both American and British English. *1,000,000,000,000,000, ...
(short scale)
barrels A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wood or metal hoops. The word vat is often used for large containers for liquids, usual ...
) without oil sands, or 595 km3 (3.74 trillion barrels) with oil sands. Consumption is currently around per day, or 4.9 km3 per year, yielding a remaining oil supply of only about 120 years, if current demand remains static. More recent studies, however, put the number at around 50 years.

# Chemistry

Petroleum is a mixture of a very large number of different
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarb ...
s; the most commonly found molecules are
alkane , the simplest alkane In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree st ...
s (paraffins),
cycloalkane In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing a ...
s (
naphthene In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing a ...
s),
aromatic hydrocarbon Aromatic compounds are those chemical compounds (most commonly organic) that contain one or more rings with pi electrons delocalized all the way around them. In contrast to compounds that exhibit aromaticity, aliphatic compounds lack this delocali ...
s, or more complicated chemicals like
asphaltene Asphaltenes are molecular substances that are found in crude oil, along with resins, aromatic hydrocarbons, and saturates (i.e. saturated hydrocarbons such as alkanes). The word "asphaltene" was coined by Boussingault in 1837 when he noticed that th ...
s. Each petroleum variety has a unique mix of
molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished ...
s, which define its physical and chemical properties, like color and
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity can be conceptualized ...
. The ''alkanes'', also known as ''paraffins'', are saturated hydrocarbons with straight or branched chains which contain only
carbon Carbon (from la, carbo "coal") is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Car ...
and
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest element in the periodic table. Hydrogen is the most abundant chemical substance in the universe, constitut ...

and have the general formula CnH2n+2. They generally have from 5 to 40 carbon atoms per molecule, although trace amounts of shorter or longer molecules may be present in the mixture. The alkanes from
pentane Pentane is an organic compound with the formula C5H12—that is, an alkane with five carbon atoms. The term may refer to any of three structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, pentane means exclusively the ''n ...
(C5H12) to
octane Octane is a hydrocarbon and an alkane with the chemical formula C8H18, and the condensed structural formula CH3(CH2)6CH3. Octane has many structural isomers that differ by the amount and location of branching in the carbon chain. One of these is ...
(C8H18) are refined into gasoline, the ones from
nonane Nonane is a linear alkane hydrocarbon with the chemical formula C9H20. It is a colorless, flammable liquid, occurring primarily in the component of the petroleum distillate fraction commonly called kerosene, which is used as a heating, tractor, and ...
(C9H20) to
hexadecane Hexadecane (also called cetane) is an alkane hydrocarbon with the chemical formula C16H34. Hexadecane consists of a chain of 16 carbon atoms, with three hydrogen atoms bonded to the two end carbon atoms, and two hydrogens bonded to each of the 14 ...
(C16H34) into
diesel fuel Diesel fuel in general is any liquid fuel specifically designed for use in diesel engines, whose fuel ignition takes place, without any spark, as a result of compression of the inlet air mixture and then injection of fuel. Therefore, diesel fuel ...
,
kerosene Kerosene, also known as paraffin, is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning "wax", and was regis ...
and
jet fuel Jet fuel or aviation turbine fuel (ATF, also abbreviated avtur) is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is colorless to straw-colored in appearance. The most commonly used fuels for commercial av ...
. Alkanes with more than 16 carbon atoms can be refined into
fuel oil Fuel oil (also known as heavy oil, marine fuel, bunker, furnace oil, or gasoil) is a fraction obtained from petroleum distillation. It includes distillates - the lighter fractions, and residues - the heavier fractions. The term ''fuel oil'' genera ...
and
lubricating oil A lubricant is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, ...
. At the heavier end of the range,
paraffin wax Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal or oil shale that consists of a mixture of hydrocarbon molecules containing between twenty and forty carbon atoms. It is solid at room temperature and begins ...
is an alkane with approximately 25 carbon atoms, while
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asph ...
has 35 and up, although these are usually
cracked Cracked may refer to: Television * ''Cracked'' (British TV series), a 2008 British comedy-drama television series that aired on STV * ''Cracked'' (Canadian TV series), a 2013 Canadian crime drama series that aired on CBC * "Cracked", a Season 8 (201 ...
by modern refineries into more valuable products. The shortest molecules, those with four or fewer carbon atoms, are in a gaseous state at room temperature. They are the petroleum gases. Depending on demand and the cost of recovery, these gases are either flared off, sold as
liquefied petroleum gas Tank cars in a Canadian train for carrying liquefied petroleum gas by rail. Liquefied petroleum gas (LPG or LP gas), is a flammable mixture of hydrocarbon gases with a mixture of 48% propane, 50% butane, and 2% pentane. LPG is used as fuel ga ...
under pressure, or used to power the refinery's own burners. During the winter, butane (C4H10), is blended into the gasoline pool at high rates, because its high vapour pressure assists with cold starts. Liquified under pressure slightly above atmospheric, it is best known for powering cigarette lighters, but it is also a main fuel source for many developing countries. Propane can be liquified under modest pressure, and is consumed for just about every application relying on petroleum for energy, from cooking to heating to transportation. The ''cycloalkanes'', also known as ''naphthenes'', are saturated hydrocarbons which have one or more carbon rings to which hydrogen atoms are attached according to the formula CnH2n. Cycloalkanes have similar properties to alkanes but have higher boiling points. The ''aromatic hydrocarbons'' are unsaturated hydrocarbons which have one or more planar six-carbon rings called
benzene ring Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, b ...
s, to which hydrogen atoms are attached with the formula CnH2n-6. They tend to burn with a sooty flame, and many have a sweet aroma. Some are
carcinogenic A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis, the formation of cancer. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substance ...
. These different molecules are separated by
fractional distillation Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation to fr ...
at an oil refinery to produce gasoline, jet fuel, kerosene, and other hydrocarbons. For example,
2,2,4-trimethylpentane 2,2,4-Trimethylpentane, also known as isooctane or iso-octane, is an organic compound with the formula (CH3)3CCH2CH(CH3)2. It is one of several isomers of octane (C8H18). This particular isomer is the standard 100 point on the octane rating scal ...
(isooctane), widely used in
gasoline Gasoline () or petrol () (see the etymology for naming differences) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines. It consists mostly of organic compoun ...
, has a chemical formula of C8H18 and it reacts with oxygen
exothermic In thermodynamics, the term exothermic process (exo- : "outside") describes a process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), ...
ally: :2 (''l'') + 25 (''g'') → 16 (''g'') + 18 (''g'') (ΔH = −5.51 MJ/mol of octane) The number of various molecules in an oil sample can be determined by laboratory analysis. The molecules are typically extracted in a
solvent A solvent (from the Latin ''solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for polar mo ...
, then separated in a
gas chromatographGas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or se ...

, and finally determined with a suitable
detector In the broadest definition, a sensor is a device, module, machine, or subsystem whose purpose is to detect events or changes in its environment and send the information to other electronics, frequently a computer processor. A sensor is always ...
, such as a
flame ionization detector A flame ionization detector (FID) is a scientific instrument that measures analytes in a gas stream. It is frequently used as a detector in gas chromatography. The measurement of ion per unit time make this a mass sensitive instrument. Standalon ...
or a
mass spectrometer Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are typically presented as a mass spectrum, a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is ...
. Due to the large number of co-eluted hydrocarbons within oil, many cannot be resolved by traditional gas chromatography and typically appear as a hump in the chromatogram. This Unresolved Complex Mixture (UCM) of hydrocarbons is particularly apparent when analysing weathered oils and extracts from tissues of organisms exposed to oil. Some of the component of oil will mix with water: the water associated fraction of the oil. Incomplete combustion of petroleum or gasoline results in production of toxic byproducts. Too little oxygen during combustion results in the formation of
carbon monoxide#REDIRECT Carbon monoxide#REDIRECT Carbon monoxide {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
. Due to the high temperatures and high pressures involved, exhaust gases from gasoline combustion in car engines usually include
nitrogen oxideNitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds: Charge-neutral *Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide * Nitrogen dioxide (NO2), nitrogen(IV) oxide *Nitrogen trioxide (NO3), ...
s which are responsible for creation of
photochemical smog Smoke fog, or smog for short, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a contraction (portmanteau) of the words smoke and fog to refer to smoky fog due to its opacity, and odor. The word ...
.

# Empirical equations for thermal properties

## Heat of combustion

At a constant volume, the heat of combustion of a petroleum product can be approximated as follows: :$Q_v = 12400 - 2100d^2$, where $Q_v$ is measured in calories per gram and $d$ is the
specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ( ...
at .

## Thermal conductivity

The
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal c ...

of petroleum based liquids can be modeled as follows: :

## Specific heat

The specific heat of petroleum oils can be modeled as follows: :

## Latent heat of vaporization

The latent heat of vaporization can be modeled under atmospheric conditions as follows: :

# Formation

## Fossil petroleum

Petroleum is a
fossil fuel A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms, containing organic molecules originating in ancient photosynthesis that release energy in combustion.Schmidt-Rohr, K. (2015). "Why C ...
derived from ancient
fossilized A fossil (from Classical Latin: , literally "obtained by digging") is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or ...
organic material Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial and aquatic environments. It is matter composed of organic compounds that have come ...
s, such as
zooplankton Zooplankton (, ) are heterotrophic (sometimes detritivorous) plankton (cf. phytoplankton). Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word ''zooplankton'' is derived from the Greek ''zoon'' (), meaning "animal ...

and
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular microa ...
. Vast amounts of these remains settled to sea or lake bottoms where they were covered in
stagnant water Water stagnation occurs when water stops flowing. Stagnant water can be a major environmental hazard. Dangers Malaria and dengue are among the main dangers of stagnant water, which can become a breeding ground for the mosquitoes that transmit the ...
(water with no dissolved
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well a ...
) or
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and ...
s such as
mud Mud is soil, loam, silt or clay mixed with water. It usually forms after rainfall or near water sources. Ancient mud deposits harden over geological time to form sedimentary rock such as shale or mudstone (generally called lutites). When geologica ...
and
silt Silt is granular material of a size between sand and clay, whose mineral origin is quartz and feldspar. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water (also known as a suspended load) and soi ...
faster than they could decompose aerobically. Approximately 1 m below this sediment, water oxygen concentration was low, below 0.1 mg/l, and anoxic conditions existed. Temperatures also remained constant. As further layers settled to the sea or lake bed, intense heat and pressure built up in the lower regions. This process caused the organic matter to change, first into a waxy material known as
kerogen Kerogen is solid, insoluble organic matter in sedimentary rocks. Consisting of an estimated 1016 tons of carbon, it is the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold. It is ...
, found in various
oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced, called shale oil. Shale oil is a substitute for conventional crude oi ...
s around the world, and then with more heat into liquid and gaseous
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarb ...
s via a process known as catagenesis. Formation of petroleum occurs from hydrocarbon
pyrolysis Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''pyro'' "fire" and ''lysis'' "separating". Pyr ...

in a variety of mainly
endothermic An endothermic process is any process with an increase in the enthalpy ''H'' (or internal energy ''U'') of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principles of Modern Chemistry'', Brooks Cole. p. 617. In such a process, a ...
reactions at high temperature or pressure, or both. These phases are described in detail below. ;Anaerobic decay: In the absence of plentiful oxygen, ''aerobic'' bacteria were prevented from decaying the organic matter after it was buried under a layer of sediment or water. However, ''anaerobic'' bacteria were able to reduce
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many are ...
s and
nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insoluble ...
s among the matter to and N2 respectively by using the matter as a source for other reactants. Due to such anaerobic bacteria, at first this matter began to break apart mostly via
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis is ...

:
polysaccharide , a beta-glucan polysaccharide Image:amylose 3Dprojection.svg">350px, Amylose is a linear polymer of glucose mainly linked with α(1→4) bonds. It can be made of several thousands of glucose units. It is one of the two components of starch, th ...
s and
protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s were hydrolyzed to
simple sugars Monosaccharides (from Greek ''monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar and the most basic units (monomers) of carbohydrates. The general formula is , albeit not all molecules fitting this for ...
and
amino acid Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), a ...
s respectively. These were further anaerobically
oxidized (mild reducing agent) are added to powdered potassium permanganate (strong oxidizing agent), a violent redox reaction accompanied by self-ignition starts. Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction in whi ...
at an accelerated rate by the
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules k ...
s of the bacteria: e.g., amino acids went through
oxidative deaminationOxidative deamination is a form of deamination that generates α-keto acids and other oxidized products from amine-containing compounds, and occurs primarily in the liver. Oxidative deamination is stereospecific, meaning it contains different stereoi ...
to
imino acid , an ''N''-substituted imino acid In chemistry, an imino acid is any molecule that contains both imine (>C=NH) and carboxyl (-C(=O)-OH) functional groups. Imino acids are related to amino acids, which contain both amino (-NH2) and carboxyl (-COO ...
s, which in turn reacted further to
ammonia Ammonia is a compound of nitrogen and hydrogen with the formula NH3. A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct characteristic of a pungent smell. It is a common nitrogenous waste, p ...
and α-keto acids.
Monosaccharide Monosaccharides (from Greek ''monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar and the most basic units (monomers) of carbohydrates. The general formula is , albeit not all molecules fitting this for ...
s in turn ultimately decayed to and
methane Methane ( or ) is a chemical compound with the chemical formula (one atom of carbon and four atoms of hydrogen). It is a group-14 hydride and the simplest alkane, and is the main constituent of natural gas. The relative abundance of methane on ...
. The anaerobic decay products of amino acids, monosaccharides,
phenols In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (—OH) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are classi ...
and
aldehyde Chemically, an aldehyde is a compound containing a functional group with the structure −CHO, consisting of a carbonyl center (a carbon double-bonded to oxygen) with the carbon atom also bonded to hydrogen and to any generic alkyl or side chain R ...
s combined to
fulvic acidFulvic acids are a family of organic acids, natural compounds, and components of the humus (which is a fraction of soil organic matter). They are similar to humic acids, with differences being the carbon and oxygen contents, acidity, degree of poly ...
s.
Fat In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds; most commonly those that occur in living beings or in food. The term often refers specifically to triglycerides (triple esters ...
s and
wax , a typical wax ester. Image:Beeswax foundation.jpg">Commercial honeycomb foundation, made by pressing beeswax between patterned metal rollers. Waxes are a diverse class of malleable_solids_near_ambient_temperatures.__They_include_higher_alkan ...
es were not extensively hydrolyzed under these mild conditions. ;Kerogen formation: Some phenolic compounds produced from previous reactions worked as
bactericide A bactericide or bacteriocide, sometimes abbreviated Bcidal, is a substance which kills bacteria. Bactericides are disinfectants, antiseptics, or antibiotics. However, material surfaces can also have bactericidal properties based solely on their ph ...
s and the
actinomycetales The Actinomycetales are an order of Actinobacteria. A member of the order is often called an actinomycete. The actinomycetes are diverse and contain a variety of subdivisions, as well as yet-unclassified isolates, mainly because some genera are ...
order of bacteria also produced antibiotic compounds (e.g.,
streptomycin Streptomycin is an antibiotic medication used to treat a number of bacterial infections. This includes tuberculosis, ''Mycobacterium avium'' complex, endocarditis, brucellosis, ''Burkholderia'' infection, plague, tularemia, and rat bite fever. F ...

). Thus the action of anaerobic bacteria ceased at about 10 m below the water or sediment. The mixture at this depth contained fulvic acids, unreacted and partially reacted fats and waxes, slightly modified
lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and ...

, resins and other hydrocarbons. As more layers of organic matter settled to the sea or lake bed, intense heat and pressure built up in the lower regions. As a consequence, compounds of this mixture began to combine in poorly understood ways to
kerogen Kerogen is solid, insoluble organic matter in sedimentary rocks. Consisting of an estimated 1016 tons of carbon, it is the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold. It is ...
. Combination happened in a similar fashion as
phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula C6H5OH. It is a white crystalline solid that is volatile. The molecule consists of a phenyl group (−C6H5) bonded to a hydroxy group (−OH). Mildly a ...
and
formaldehyde Formaldehyde ( , also ) (systematic name methanal) is a naturally occurring organic compound with the formula CH2O (H−CHO). The pure compound is a pungent-smelling colourless gas that polymerises spontaneously into paraformaldehyde (refer to s ...
molecules react to urea-formaldehyde resins, but kerogen formation occurred in a more complex manner due to a bigger variety of reactants. The total process of kerogen formation from the beginning of anaerobic decay is called diagenesis, a word that means a transformation of materials by dissolution and recombination of their constituents. ;Transformation of kerogen into fossil fuels: Kerogen formation continued to the depth of about 1 km from the Earth's surface where temperatures may reach around 50 °C. Kerogen formation represents a halfway point between organic matter and fossil fuels: kerogen can be exposed to oxygen, oxidize and thus be lost or it could be buried deeper inside the
Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper ...
and be subjected to conditions which allow it to slowly transform into fossil fuels like petroleum. The latter happened through catagenesis in which the reactions were mostly
radical Radical may refer to: Arts and entertainment Music *''Radical'' (mixtape), by Odd Future, 2010 *''Radical'' (Smack album), 1988 *"Radicals", a song by Tyler, The Creator from the 2011 album ''Goblin'' Architecture and design * Radical period (d ...
rearrangements of kerogen. These reactions took thousands to millions of years and no external reactants were involved. Due to radical nature of these reactions, kerogen reacted towards two classes of products: those with low H/C ratio (
anthracene Anthracene is a solid polycyclic aromatic hydrocarbon (PAH) of formula C14H10, consisting of three fused benzene rings. It is a component of coal tar. Anthracene is used in the production of the red dye alizarin and other dyes. Anthracene is colorl ...
or products similar to it) and those with high H/C ratio (
methane Methane ( or ) is a chemical compound with the chemical formula (one atom of carbon and four atoms of hydrogen). It is a group-14 hydride and the simplest alkane, and is the main constituent of natural gas. The relative abundance of methane on ...
or products similar to it); i.e., carbon-rich or hydrogen-rich products. Because catagenesis was closed off from external reactants, the resulting composition of the fuel mixture was dependent on the composition of the kerogen via reaction
stoichiometry Stoichiometry is the calculation of reactants and products in chemical reactions in chemistry. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products, leading to ...
. 3 main types of kerogen exist: type I (algal), II (liptinic) and III (humic), which were formed mainly from
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular microa ...
,
plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucial ...
and
woody plant A woody plant is a plant that produces wood as its structural tissue and thus has a hard stem. In cold climates, woody plants further survive winter or dry season above ground, as opposite to herbaceous plants that die back to the ground until spr ...
s (this term includes
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that ...

s,
shrub A shrub (or bush, but this is more of a gardening term) is a small- to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be deciduous or evergreen. They are distinguish ...
s and
liana A liana is a long-stemmed, woody vine that is rooted in the soil at ground level and uses trees, as well as other means of vertical support, to climb up to the canopy in search of direct sunlight. Lianas are characteristic of tropical moist d ...
s) respectively. Catagenesis was
pyrolytic Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''pyro'' "fire" and ''lysis'' "separating". Pyr ...

despite of the fact that it happened at relatively low temperatures (when compared to commercial pyrolysis plants) of 60 to several hundred °C. Pyrolysis was possible because of the long reaction times involved. Heat for catagenesis came from the decomposition of
radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...
materials of the crust, especially 40K, 232Th, 235U and 238U. The heat varied with
geothermal gradient ). Geothermal gradient is the rate of temperature change with respect to increasing depth in Earth's interior. As a general rule, the crust temperature is rising with depth due to the heat flow from the much hotter mantle; away from tectonic pla ...
and was typically 10-30 °C per km of depth from the Earth's surface. Unusual
magma 300px, Hawaii. Lava is the extrusive">Hawaii (island)">Hawaii. Lava is the extrusive equivalent of magma. Magma (from Ancient Greek μάγμα (''mágma'') meaning "thick unguent") is the molten or semi-molten natural material from which al ...
intrusions, however, could have created greater localized heating. Geologists often refer to the temperature range in which oil forms as an "oil window". Below the minimum temperature oil remains trapped in the form of kerogen. Above the maximum temperature the oil is converted to natural gas through the process of
thermal crackingIn petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of ca ...
. Sometimes, oil formed at extreme depths may migrate and become trapped at a much shallower level. The
Athabasca Oil Sands#REDIRECT Athabasca oil sands#REDIRECT Athabasca oil sands {{R from other capitalisation ...
{{R from other capitalisation ...

are one example of this.

## Abiogenic petroleum

An alternative mechanism to the one described above was proposed by Russian scientists in the mid-1850s, the hypothesis of
abiogenic petroleum originAbiogenic petroleum origin is a body of hypotheses which propose that petroleum and natural gas deposits are mostly formed by inorganic means, rather than by the decomposition of organisms. Thomas Gold's ''deep gas hypothesis'' states that some natur ...
(petroleum formed by inorganic means), but this is contradicted by geological and
geochemical Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the en ...
evidence. Abiogenic sources of oil have been found, but never in commercially profitable amounts. "The controversy isn't over whether abiogenic oil reserves exist," said Larry Nation of the American Association of Petroleum Geologists. "The controversy is over how much they contribute to Earth's overall reserves and how much time and effort geologists should devote to seeking them out."

# Reservoirs

Three conditions must be present for oil reservoirs to form: * a
source rockIn petroleum geology, source rock is rock which has generated hydrocarbons or which could generate hydrocarbons. Source rocks are one of the necessary elements of a working petroleum system. They are organic-rich sediments that may have been deposite ...
rich in
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarb ...
material buried deeply enough for subterranean heat to cook it into oil, * a
porousPorosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure the ...
and
permeable Permeability, permeable, and semipermeable may refer to: Chemistry *Semipermeable membrane, a membrane which will allow certain molecules or ions to pass through it by diffusion *Vascular permeability, the movement of fluids and molecules betwee ...
reservoir rock where it can accumulate, * a
caprockCaprock or cap rock is a harder or more resistant rock type overlying a weaker or less resistant rock type.Kearey, Philip (2001). ''Dictionary of Geology'', 2nd ed., Penguin Reference, London, New York, etc., p. 41.. . Common types of caprock are sa ...
(seal) or other mechanism to prevent the oil from escaping to the surface. Within these reservoirs, fluids will typically organize themselves like a three-layer cake with a layer of water below the oil layer and a layer of gas above it, although the different layers vary in size between reservoirs. Because most hydrocarbons are less dense than rock or
water Water is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent). It is vita ...
, they often migrate upward through adjacent rock layers until either reaching the surface or becoming trapped within porous rocks (known as
reservoirs A reservoir (; from French ''réservoir'' ) is most commonly an enlarged natural or artificial lake created using a dam to store water. Reservoirs can be created in a number of ways, including controlling a watercourse that drains an existing ...
) by impermeable rocks above. However, the process is influenced by underground water flows, causing oil to migrate hundreds of kilometres horizontally or even short distances downward before becoming trapped in a reservoir. When hydrocarbons are concentrated in a trap, an
oil field A petroleum reservoir or oil and gas reservoir is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. Petroleum reservoirs are broadly classified as ''conventional'' and ''unconventional'' reservoirs. In conventiona ...

forms, from which the liquid can be extracted by
drill A drill or drilling machine is a tool primarily used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driver, depending on application, secured by a chuck. Some powered drills also include a hammer funct ...
ing and
pump near the Hengsteysee, GermanyA pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups ...
ing. The reactions that produce oil and natural gas are often modeled as first order breakdown reactions, where hydrocarbons are broken down to oil and natural gas by a set of parallel reactions, and oil eventually breaks down to natural gas by another set of reactions. The latter set is regularly used in
petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sour ...
plants and
oil refineries An oil refinery or petroleum refinery is an industrial process plant where crude oil is transformed and refined into useful products such as petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, je ...
. Petroleum has mostly been recovered by
oil drilling , such as this one located south of Midland, Texas, is a common sight in West Texas An oil well is a boring (earth), boring in the Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as as ...
(natural petroleum springs are rare). Drilling is carried out after studies of structural geology (at the reservoir scale), sedimentary basin analysis, and reservoir characterisation (mainly in terms of the
porosityPorosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure the ...
and permeability of geologic reservoir structures). Recent improvements to technologies have also led to exploitation of other unconventional reserves such as
oil sands Tar sandstone from United_States.html"_style="text-decoration:_none;"class="mw-redirect"_title="California,_United_States">California,_United_States_ Oil_sands,_tar_sands,_crude_bitumen,_or_bituminous_sands,_are_a_type_of_unconventional ...
and
oil shale Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced, called shale oil. Shale oil is a substitute for conventional crude oi ...
. Wells are drilled into oil reservoirs to extract the crude oil. "Natural lift" production methods that rely on the natural reservoir pressure to force the oil to the surface are usually sufficient for a while after reservoirs are first tapped. In some reservoirs, such as in the Middle East, the natural pressure is sufficient over a long time. The natural pressure in most reservoirs, however, eventually dissipates. Then the oil must be extracted using "
artificial liftArtificial lift refers to the use of artificial means to increase the flow of liquids, such as crude oil or water, from a production well. Generally this is achieved by the use of a mechanical device inside the well (known as pump or velocity string) ...
" means. Over time, these "primary" methods become less effective and "secondary" production methods may be used. A common secondary method is "waterflood" or injection of water into the reservoir to increase pressure and force the oil to the drilled shaft or "wellbore." Eventually "tertiary" or "enhanced" oil recovery methods may be used to increase the oil's flow characteristics by injecting steam, carbon dioxide and other gases or chemicals into the reservoir. In the United States, primary production methods account for less than 40 percent of the oil produced on a daily basis, secondary methods account for about half, and tertiary recovery the remaining 10 percent. Extracting oil (or "bitumen") from oil/tar sand and oil shale deposits requires mining the sand or shale and heating it in a vessel or retort, or using "in-situ" methods of injecting heated liquids into the deposit and then pumping the liquid back out saturated with oil.

## Unconventional oil reservoirs

Oil-eating bacteria
biodegrade Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. Mechanisms The process of biodegradation can be divided into three stages: biodeterioration, biofragmentation, and assimilation. Biodeterioration is ...
oil that has escaped to the surface.
Oil sands Tar sandstone from United_States.html"_style="text-decoration:_none;"class="mw-redirect"_title="California,_United_States">California,_United_States_ Oil_sands,_tar_sands,_crude_bitumen,_or_bituminous_sands,_are_a_type_of_unconventional ...
are reservoirs of partially biodegraded oil still in the process of escaping and being biodegraded, but they contain so much migrating oil that, although most of it has escaped, vast amounts are still present—more than can be found in conventional oil reservoirs. The lighter fractions of the crude oil are destroyed first, resulting in reservoirs containing an extremely heavy form of crude oil, called crude bitumen in Canada, or extra-heavy crude oil in
Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in the Ca ...
. These two countries have the world's largest deposits of oil sands. On the other hand,
oil shales Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced, called shale oil. Shale oil is a substitute for conventional crude oi ...
are source rocks that have not been exposed to heat or pressure long enough to convert their trapped hydrocarbons into crude oil. Technically speaking, oil shales are not always shales and do not contain oil, but are fined-grain sedimentary rocks containing an insoluble organic solid called
kerogen Kerogen is solid, insoluble organic matter in sedimentary rocks. Consisting of an estimated 1016 tons of carbon, it is the most abundant source of organic compounds on earth, exceeding the total organic content of living matter 10,000-fold. It is ...
. The kerogen in the rock can be converted into crude oil using heat and pressure to simulate natural processes. The method has been known for centuries and was patented in 1694 under British Crown Patent No. 330 covering, "A way to extract and make great quantities of pitch, tar, and oil out of a sort of stone." Although oil shales are found in many countries, the United States has the world's largest deposits.

# Classification

The
petroleum industry The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of exploration, extraction, refining, transporting (often by oil tankers and pipelines), and marketing of petroleum products. The largest volum ...
generally classifies crude oil by the geographic location it is produced in (e.g.,
West Texas Intermediate West Texas Intermediate (WTI) can refer to a grade or a mix of crude oil, and/or the spot price, the futures price, or the assessed price for that oil; colloquially WTI usually refers to the price of the New York Mercantile Exchange (NYMEX) WTI Cr ...
,
Brent Brent may refer to: *Brent (name), an English given and surname Place name ;In the United States *Brent, Alabama *Brent, Florida *Brent, Georgia *Brent, Missouri, a ghost town *Brent, Oklahoma ;In the United Kingdom * Brent, Cornwall *Brent K ...
, or
Oman Oman ( ; ar, عُمَان ' ), officially the Sultanate of Oman ( ar, سلْطنةُ عُمان ), is a country on the southeastern coast of the Arabian Peninsula in Western Asia and the oldest independent state in the Arab world. Located in a s ...
), its
API gravityThe American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks. ...
(an oil industry measure of density), and its sulfur content. Crude oil may be considered ''
light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nm, between the inf ...
'' if it has low density, ''
heavy Heavy may refer to: Measures * Heavy (aeronautics), a term used by pilots and air traffic controllers to refer to aircraft capable of 300,000 lbs or more takeoff weight * Heavy, a characterization of objects with substantial weight * Heavy, a ...
'' if it has high density, or ''medium'' if it has a density between that of ''light'' and ''heavy''. Additionally, it may be referred to as ''
sweet Sweetness is a basic taste most commonly perceived when eating foods rich in sugars. Sweet tastes are generally regarded as pleasurable, except when in excess. In addition to sugars like sucrose, many other chemical compounds are sweet, includin ...
'' if it contains relatively little sulfur or ''
sour The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ce ...
'' if it contains substantial amounts of sulfur. The geographic location is important because it affects transportation costs to the refinery. ''Light'' crude oil is more desirable than ''heavy'' oil since it produces a higher yield of gasoline, while ''sweet'' oil commands a higher price than ''sour'' oil because it has fewer environmental problems and requires less refining to meet sulfur standards imposed on fuels in consuming countries. Each crude oil has unique molecular characteristics which are revealed by the use of
Crude oil assay Crude can refer to: * Crude oil or simply crude, the unprocessed form of petroleum * ''Crude'' (2007 film), an Australian documentary about the geology and economics of crude oil * ''Crude'' (2009 film), an American documentary about oil companies ...
analysis in petroleum laboratories.
Barrels A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wood or metal hoops. The word vat is often used for large containers for liquids, usual ...
from an area in which the crude oil's molecular characteristics have been determined and the oil has been classified are used as pricing
references Reference is a relationship between objects in which one object designates, or acts as a means by which to connect to or link to, another object. The first object in this relation is said to ''refer to'' the second object. It is called a ''name'' ...
throughout the world. Some of the common reference crudes are: *
West Texas Intermediate West Texas Intermediate (WTI) can refer to a grade or a mix of crude oil, and/or the spot price, the futures price, or the assessed price for that oil; colloquially WTI usually refers to the price of the New York Mercantile Exchange (NYMEX) WTI Cr ...
(WTI), a very high-quality, sweet, light oil delivered at
Cushing, Oklahoma Cushing is a city in Payne County, Oklahoma, United States. The population was 7,826 at the time of the 2010 census, a decline of 6.5% since 8,371 in 2000. Cushing was established after the Land Run of 1891 by William "Billy Rae" Little. It was n ...
for North American oil * Brent Blend, consisting of 15 oils from fields in the
Brent Brent may refer to: *Brent (name), an English given and surname Place name ;In the United States *Brent, Alabama *Brent, Florida *Brent, Georgia *Brent, Missouri, a ghost town *Brent, Oklahoma ;In the United Kingdom * Brent, Cornwall *Brent K ...
and
Ninian Ninian is a Christian saint, first mentioned in the 8th century as being an early missionary among the Pictish peoples of what is now Scotland. For this reason he is known as the Apostle to the Southern Picts, and there are numerous dedications ...
systems in the
East Shetland Basin The East Shetland Basin is a major oil-producing area of the North Sea between Scotland and Norway. Oil produced in the UK area is landed at Sullom Voe Terminal in the Shetland Islands. Associated gas flows via the FLAGS pipeline to St Fergus Gas ...
of the
North Sea The North Sea is a sea of the Atlantic Ocean located between Great Britain (England and Scotland), Denmark, Norway, Germany, the Netherlands, Belgium and France. An epeiric (or "shelf") sea on the European continental shelf, it connects to the o ...
. The oil is landed at
Sullom Voe File:StarLocatorDot.gif Sullom Voe is an inlet of the North Sea between the parishes of Delting and Northmavine in Shetland, Scotland. It is a location of the Sullom Voe oil terminal and Shetland Gas Plant. The word Voe is from the Old Norse ' a ...

terminal in
Shetland Shetland ( on, Hjaltland; sco, Shetland; nrn, Hjetland), also called the Shetland Islands and formerly Zetland, is a subarctic archipelago in the Northern Isles of Scotland, situated in the Northern Atlantic, between Great Britain, the Faroe Is ...
. Oil production from Europe, Africa and Middle Eastern oil flowing West tends to be priced off this oil, which forms a
benchmark Benchmark may refer to: Measurements and other evaluations *Benchmarking, evaluating performance within organizations *Reference points for geographic measurements: **Benchmark (surveying), a point of known elevation marked for the purpose of su ...
* Dubai-Oman, used as benchmark for Middle East sour crude oil flowing to the Asia-Pacific region * Tapis (from
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federal constitutional monarchy consists of thirteen states and three federal territories, separated by the South China Sea into two regions, Peninsular Malaysia and Borneo's East Malaysia. Pe ...

, used as a reference for light Far East oil) * Minas (from
Indonesia Indonesia ( ), officially the Republic of Indonesia ( id, Republik Indonesia, links=yes ), is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of more than seventeen thousand islands, including Sumatra, ...

, used as a reference for heavy Far East oil) * The
OPEC Reference BasketThe OPEC Reference Basket (ORB), also referred to as the OPEC Basket, is a weighted average of prices for petroleum blends produced by OPEC members. It is used as an important benchmark for crude oil prices. OPEC has often attempted to keep the price ...
, a weighted average of oil blends from various
OPEC The Organization of the Petroleum Exporting Countries (OPEC, ) is an intergovernmental organization of countries. Founded on 14 September 1960 in Baghdad by the first five members (Iran, Iraq, Kuwait, Saudi Arabia, and Venezuela), it has si ...

(The Organization of the Petroleum Exporting Countries) countries * Midway Sunset Heavy, by which heavy oil in California is priced *
Western Canadian Select Western Canadian Select (WCS) is a heavy sour blend of crude oil that is one of North America's largest heavy crude oil streams. It was established in December 2004 as a new heavy oil stream by EnCana (now Cenovus Energy Inc.), Canadian Natural R ...
the benchmark crude oil for emerging heavy, high TAN (acidic) crudes. There are declining amounts of these benchmark oils being produced each year, so other oils are more commonly what is actually delivered. While the reference price may be for West Texas Intermediate delivered at Cushing, the actual oil being traded may be a discounted Canadian heavy oil—Western Canadian Select—delivered at Hardisty,
Alberta ("Strong and free") , image_map = Alberta in Canada 2.svg , Label_map = yes , coordinates = , official_lang = English , capital = Edmonton , largest_city = Calgary , l ...
, and for a Brent Blend delivered at Shetland, it may be a discounted Russian Export Blend delivered at the port of Primorsk. Once extracted, oil is refined and separated, most easily by
distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. Dry distillation is the heating of solid materials to produce gaseous products ...
, into numerous products for direct use or use in manufacturing, such as
gasoline Gasoline () or petrol () (see the etymology for naming differences) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines. It consists mostly of organic compoun ...
(petrol), diesel and
kerosene Kerosene, also known as paraffin, is a combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in aviation as well as households. Its name derives from el, κηρός (''keros'') meaning "wax", and was regis ...
to
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asph ...
and chemical
reagent 200px, Reactants, such as sulfur (''pictured''), are the starting materials that are used in chemical reactions. A reagent is a substance or compound added to a system to cause a chemical reaction, or added to test if a reaction occurs. The terms ...
s (
ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or H2C=CH2. It is a colorless flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...

,
propylene Propene, also known as propylene or methyl ethylene, is an unsaturated organic compound with the chemical formula C3H6. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a f ...
,
buteneButene, also known as butylene, is an alkene with the formula C4H8. The word ''butene'' may refer to any of the individual compounds. They are colourless gases that are present in crude oil as a minor constituent in quantities that are too small fo ...
,
acrylic acid Acrylic acid (IUPAC: propenoic acid) is an organic compound with the formula CH2=CHCOOH. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has a char ...
, para-xylene) used to make
plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptability, ...
s,
pesticide Pesticides are substances that are meant to control pests. The term pesticide includes all of the following: herbicide, insecticides (which may include insect growth regulators, termiticides, etc.) nematicide, molluscicide, piscicide, avicide, ...
s and
pharmaceuticals A medication (also referred to as medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy (pharmacotherapy) is an important part of the medical field and relies on ...
.

# Industry

## Transport

In the 1950s, shipping costs made up 33 percent of the price of oil transported from the
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=Xalij-e Fârs, lit=Gulf of Fars, ) is a mediterranean sea in Western Asia. The body of water is an extension of the Indian Ocean (Gulf of Oman) through the Strait of Hormuz and lies between Iran ...
to the United States, but due to the development of
supertankers An oil tanker, also known as a petroleum tanker, is a ship designed for the bulk transport of oil or its products. There are two basic types of oil tankers: crude tankers and product tankers. Crude tankers move large quantities of unrefined crude ...
in the 1970s, the cost of shipping dropped to only 5 percent of the price of Persian oil in the US. Due to the increase of the value of the crude oil during the last 30 years, the share of the shipping cost on the final cost of the delivered commodity was less than 3% in 2010.

# Uses

The chemical structure of petroleum is
heterogeneous Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, size, we ...
, composed of hydrocarbon chains of different lengths. Because of this, petroleum may be taken to
oil refineries An oil refinery or petroleum refinery is an industrial process plant where crude oil is transformed and refined into useful products such as petroleum naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, liquefied petroleum gas, je ...
and the hydrocarbon chemicals separated by
distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. Dry distillation is the heating of solid materials to produce gaseous products ...
and treated by other
chemical process In a scientific sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. Such a chemical process can occur by itself or be caused by an outside force, and involves a chemical reaction of some s ...
es, to be used for a variety of purposes. The total cost per plant is about 9 billion dollars.

## Fuels

The most common distillation fractions of petroleum are
fuel A fuel is any material that can be made to react with other substances so that it releases energy as heat energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but has ...
s. Fuels include (by increasing boiling temperature range): Petroleum classification according to chemical composition.

## Other derivatives

Certain types of resultant hydrocarbons may be mixed with other non-hydrocarbons, to create other end products: * Alkenes (olefins), which can be manufactured into plastics or other compounds * Lubricants (produces light machine oils, motor oils, and Grease (lubricant), greases, adding
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity can be conceptualized ...
stabilizers as required) * Wax, used in the packaging of frozen foods, among others * Sulfur or sulfuric acid. These are useful industrial materials. Sulfuric acid is usually prepared as the acid precursor oleum, a byproduct of Hydrodesulfurization, sulfur removal from fuels. * Bulk tar * Asphalt * Petroleum coke, used in speciality carbon products or as solid fuel * Paraffin wax * Aromatic
petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sour ...
s to be used as precursors in other
chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., witho ...
production

## Agriculture

Since the 1940s, agricultural productivity has increased dramatically, due largely to the increased use of energy-intensive mechanization,
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from li ...
s and
pesticide Pesticides are substances that are meant to control pests. The term pesticide includes all of the following: herbicide, insecticides (which may include insect growth regulators, termiticides, etc.) nematicide, molluscicide, piscicide, avicide, ...
s.

# Use by country

## Consumption statistics

File:Global Carbon Emissions.svg, Global fossil carbon emissions, an indicator of consumption, from 1800. File:World energy consumption.svg, Rate of world energy usage per year from 1970.BP
Statistical Review of World Energy
, Workbook (xlsx), London, 2012
File:Oil consumption per day by region from 1980 to 2006.svg, Daily oil consumption from 1980 to 2006. File:Oil consumption per day by region from 1980 to 2006 solid3.svg, Oil consumption by percentage of total per region from 1980 to 2006: . File:World oil consumption 1980 to 2007 by region.svg, Oil consumption 1980 to 2007 by region.

## Consumption

According to the US Energy Information Administration (EIA) estimate for 2017, the world consumes 98.8 million barrels of oil each day. This table orders the amount of petroleum consumed in 2011 in thousand
barrels A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wood or metal hoops. The word vat is often used for large containers for liquids, usual ...
(1000 bbl) per day and in thousand cubic metres (1000 m3) per day: Source
Population Data: 1 Peak oil, peak production of oil already passed in this state 2 This country is not a major oil producer

## Production

In petroleum industry parlance, ''production'' refers to the quantity of crude extracted from reserves, not the literal creation of the product.

## Exportation

In order of net exports in 2011, 2009 and 2006 in thousand Barrel (unit), bbl/Day, d and thousand m3/d: Source
1 Peak oil, peak production already passed in this state 2 Canadian statistics are complicated by the fact it is both an importer and exporter of crude oil, and refines large amounts of oil for the U.S. market. It is the leading source of U.S. imports of oil and products, averaging in August 2007. Total world production/consumption (as of 2005) is approximately .

## Importation

In order of net imports in 2011, 2009 and 2006 in thousand Barrel (unit), bbl/Day, d and thousand m3/d: Source

## Non-producing consumers

Countries whose oil production is 10% or less of their consumption. Source

# Environmental effects

Because petroleum is a naturally occurring substance, its presence in the environment need not be the result of human causes such as accidents and routine activities (seismology, seismic exploration, Boring (earth), drilling, extraction, refining and combustion). Phenomena such as petroleum seep, seeps and tar pits are examples of areas that petroleum affects without man's involvement. Regardless of source, petroleum's effects when released into the environment are similar.

## Climate change

, about a quarter of annual global
greenhouse gas A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxid ...
emissions is the carbon dioxide from burning petroleum (plus methane leaks from the industry). Along with the burning of coal, petroleum combustion is the largest contributor to the increase in atmospheric CO2. Atmospheric CO2 has risen over the last 150 years to current levels of over 415 Parts-per notation, ppmv, from the Carbon dioxide in Earth's atmosphere#Past concentration, 180–300 ppmv of the prior 800 thousand years. This rise in temperature has reduced the minimum Arctic ice pack to , a loss of almost half since satellite measurements started in 1979. Ocean acidification is the increase in the acidity of the Earth's oceans caused by the uptake of carbon dioxide () from the Earth's atmosphere, atmosphere. This increase in acidity inhibits all marine life—having a greater impact on smaller organisms as well as shelled organisms (see scallops).

## Extraction

Oil extraction is simply the removal of oil from the reservoir (oil pool). Oil is often recovered as a water-in-oil emulsion, and specialty chemicals called demulsifiers are used to separate the oil from water. Oil extraction is costly and often environmentally damaging. Offshore exploration and extraction of oil disturb the surrounding marine environment.

## Oil spills

Crude oil and refined fuel Oil spill, spills from tanker (ship), tanker ship accidents have damaged natural ecosystems and human livelihoods in Alaska, the Gulf of Mexico, the Galápagos Islands, France and many List of oil spills, other places. The quantity of oil spilled during accidents has ranged from a few hundred tons to several hundred thousand tons (e.g., Deepwater Horizon oil spill, SS Atlantic Empress, Amoco Cadiz). Smaller spills have already proven to have a great impact on ecosystems, such as the Exxon Valdez oil spill, ''Exxon Valdez'' oil spill. Oil spills at sea are generally much more damaging than those on land, since they can spread for hundreds of nautical miles in a thin oil slick which can cover beaches with a thin coating of oil. This can kill sea birds, mammals, shellfish and other organisms it coats. Oil spills on land are more readily containable if a makeshift earth dam can be rapidly bulldozed around the spill site before most of the oil escapes, and land animals can avoid the oil more easily. Control of oil spills is difficult, requires ad hoc methods, and often a large amount of manpower. The dropping of bombs and incendiary devices from aircraft on the wreck produced poor results; modern techniques would include pumping the oil from the wreck, like in the Prestige oil spill, ''Prestige'' oil spill or the MV Erika, ''Erika'' oil spill. Though crude oil is predominantly composed of various hydrocarbons, certain nitrogen heterocyclic compounds, such as pyridine, picoline, and quinoline are reported as contaminants associated with crude oil, as well as facilities processing oil shale or coal, and have also been found at legacy creosote, wood treatment sites. These compounds have a very high water solubility, and thus tend to dissolve and move with water. Certain naturally occurring bacteria, such as ''Micrococcus'', ''Arthrobacter'', and ''Rhodococcus'' have been shown to degrade these contaminants.

## Tarballs

A tarball is a blob of crude oil (not to be confused with tar, which is a man-made product derived from pine trees or refined from petroleum) which has been weathered after floating in the ocean. Tarballs are an aquatic pollutant in most environments, although they can occur naturally, for example in the Santa Barbara Channel of California or in the Gulf of Mexico off Texas. Their concentration and features have been used to assess the extent of oil spills. Their composition can be used to identify their sources of origin, and tarballs themselves may be dispersed over long distances by deep sea currents. They are slowly decomposed by bacteria, including ''Chromobacterium violaceum'', ''Cladosporium resinae'', ''Bacillus submarinus'', ''Micrococcus varians'', ''Pseudomonas aeruginosa'', ''Candida marina'' and ''Saccharomyces estuari''.

## Whales

James S. Robbins has argued that the advent of petroleum-refined kerosene saved some species of great whales from extinction by providing an inexpensive substitute for whale oil, thus eliminating the economic imperative for open-boat whaling.

# Alternatives

In the United States in 2007 about 70 percent of petroleum was used for transportation (e.g. gasoline, diesel, jet fuel), 24 percent by industry (e.g. production of plastics), 5 percent for residential and commercial uses, and 2 percent for electricity production. Outside of the US, a higher proportion of petroleum tends to be used for electricity.

## Vehicle fuels

Petroleum-based vehicle fuels can be replaced by either alternative fuels, or other methods of propulsion such as Electric motor, electric or Nuclear power, nuclear. Alternative fuel vehicles refers to both: * Vehicles that use alternative fuels used in standard or modified
internal combustion engine An internal combustion engine (ICE) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, t ...
s such as natural gas vehicles, neat ethanol vehicles, flexible-fuel vehicles, biodiesel-powered vehicles, propane autogas, and Hydrogen internal combustion engine vehicle, hydrogen vehicles. * Vehicles with advanced propulsion systems that reduce or substitute petroleum use such as battery electric vehicles, plug-in hybrid electric vehicles, hybrid electric vehicles, and hydrogen vehicle, hydrogen fuel cell vehicles.

## Industrial oils

Biological feedstocks do exist for industrial uses such as Bioplastic production.

## Electricity

In oil producing countries with little refinery capacity, oil is sometimes burned to produce electricity.

# International relations

Control of petroleum production has been a significant driver of international relations during much of the 20th and 21st centuries. Organizations like OPEC have played an outsized role in international politics. Some historians and commentators have called this the "Age of Oil" With the rise of
renewable energy Renewable energy is useful energy that is collected from renewable resources, which are naturally replenished on a human timescale, including carbon neutral sources like sunlight, wind, rain, tides, waves, and geothermal heat. The term often a ...
and addressing climate change some commentators expect a realignment of international power away from petrostates.

## Conflict

Petroleum production is tightly linked with conflict: whether through direct aggression such as the U.S. invasion of Iraq, trade wars such as 2020 Russia–Saudi Arabia oil price war, the 2020 Russia–Saudi Arabia oil price war, or by fueling conflict in regions such as funding
Islamic State of Iraq and the Levant {{Infobox war faction , name = Islamic State of Iraq and the Levant , native_name = {{rtl-lang, ar, الدولة الإسلامية في العراق والشام''{{transl, ar, ad-Dawlah al-Islāmiyah fī 'l-ʿIrāq wa-sh-Shām'' , war = the Iraq ...
in the Syrian civil war.

# Future production

Consumption function, Consumption in the twentieth and twenty-first centuries has been abundantly pushed by automobile sector growth. The 1980s oil glut, 1985–2003 oil glut even fueled the sales of low fuel economy vehicles in OECD countries. The 2008 economic crisis seems to have had some impact on the sales of such vehicles; still, in 2008 oil consumption showed a small increase. In 2016 Goldman Sachs predicted lower demand for oil due to emerging economies concerns, especially China. The BRICS (Brasil, Russia, India, China, South Africa) countries might also kick in, as China briefly was the first automobile market in December 2009. In the long term, uncertainties linger; the
OPEC The Organization of the Petroleum Exporting Countries (OPEC, ) is an intergovernmental organization of countries. Founded on 14 September 1960 in Baghdad by the first five members (Iran, Iraq, Kuwait, Saudi Arabia, and Venezuela), it has si ...

believes that the OECD countries will push low consumption policies at some point in the future; when that happens, it will definitely curb oil sales, and both OPEC and the Energy Information Administration (EIA) kept lowering their 2020 consumption estimates during the past five years. A detailed review of International Energy Agency oil projections have revealed that revisions of world oil production, price and investments have been motivated by a combination of demand and supply factors. All together, Non-OPEC conventional projections have been fairly stable the last 15 years, while downward revisions were mainly allocated to OPEC. Recent upward revisions are primarily a result of US tight oil. Production will also face an increasingly complex situation; while OPEC countries still have large reserves at low production prices, newly found reservoirs often lead to higher prices; offshore giants such as Tupi oil field, Tupi, Guara and Tiber oilfield, Tiber demand high investments and ever-increasing technological abilities. Subsalt reservoirs such as Tupi were unknown in the twentieth century, mainly because the industry was unable to probe them. Enhanced Oil Recovery (EOR) techniques (example: Daqing Field, DaQing, China) will continue to play a major role in increasing the world's recoverable oil. The expected availability of petroleum resources has always been around 35 years or even less since the start of the modern exploration. The oil constant, an insider pun in the German industry, refers to that effect. A growing number of divestment campaigns from major funds pushed by newer generations who question the sustainability of petroleum may hinder the financing of future oil prospection and production.

## Peak oil

Peak oil is a term applied to the projection that future petroleum production (whether for individual oil wells, entire oil fields, whole countries, or worldwide production) will eventually peak and then decline at a similar rate to the rate of increase before the peak as these reserves are exhausted. The peak of oil discoveries was in 1965, and oil production per year has surpassed oil discoveries every year since 1980. However, this does not mean that potential oil production has surpassed oil demand. It is difficult to predict the oil peak in any given region, due to the lack of knowledge and/or transparency in accounting of global oil reserves. Based on available production data, proponents have previously predicted the peak for the world to be in years 1989, 1995, or 1995–2000. Some of these predictions date from before the recession of the early 1980s, and the consequent reduction in global consumption, the effect of which was to delay the date of any peak by several years. Just as the 1971 U.S. peak in oil production was only clearly recognized after the fact, a peak in world production will be difficult to discern until production clearly drops off. The peak is also a moving target as it is now measured as "liquids", which includes synthetic fuels, instead of just conventional oil. In 2020, according to BP#Climate policy, BP's Energy Outlook 2020, peak oil had been reached, due to the changing energy landscape coupled with the Financial market impact of the COVID-19 pandemic#Oil prices, economic toll of the COVID-19 pandemic. While there has been much focus historically on peak oil supply, focus is increasingly shifting to peak demand as more countries seek to transition to renewable energy. The GeGaLo index of geopolitical gains and losses assesses how the geopolitical position of 156 countries may change if the world fully transitions to renewable energy resources. Former oil exporters are expected to lose power, while the positions of former oil importers and countries rich in renewable energy resources is expected to strengthen.

## Unconventional oil

Unconventional oil is petroleum produced or extracted using techniques other than the conventional methods. The calculus for peak oil has changed with the introduction of unconventional production methods. In particular, the combination of
horizontal drilling Directional drilling (or slant drilling) is the practice of drilling non-vertical bores. It can be broken down into four main groups: oilfield directional drilling, utility installation directional drilling (horizontal directional drilling), dire ...
and
hydraulic fracturing#REDIRECT Hydraulic fracturing {{R from other capitalisation ...
has resulted in a significant increase in production from previously uneconomic plays. Analysts expected that \$150 billion would be spent on further developing North American tight oil fields in 2015. The large increase in tight oil production is one of the reasons behind the price drop in late 2014.In English
''Teknisk Ukeblad'', 11 December 2014. Accessed: 11 December 2014.
Certain rock strata contain hydrocarbons but have low permeability and are not thick from a vertical perspective. Conventional vertical wells would be unable to economically retrieve these hydrocarbons. Horizontal drilling, extending horizontally through the strata, permits the well to access a much greater volume of the strata. Hydraulic fracturing creates greater permeability and increases hydrocarbon flow to the wellbore.

* Barrel of oil equivalent * Filling station * Gas oil ratio * List of oil exploration and production companies * List of oil fields * Manure-derived synthetic crude oil * Oil burden * Petroleum geology * Petroleum politics * Petrocurrency * Thermal depolymerization * Total petroleum hydrocarbon * Waste oil

# References

* * translated 1955 * * * * * * * Mirbabayev M.F.(2017).Brief history of the first drilled oil well;and the people involved.-"Oil-Industry History"(US),vol.18,#1, p. 25-34.

* Antonia Juhasz, Juhasz, Antonia, "The End of OIL?: The COVID-19 pandemic, pandemic has battered an already struggling oil industry. Whether it survives is up to us", ''Sierra Magazine'', vol. 105, no. 5 (September / October 2020), pp. 36–40, 51. *