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[[File:Oil well.jpg|thumb|[[Pumpjack]] pumping an oil well near [[Lubbok, Texas]].]]
[[File:Oil Reserves.png|thumb|400px|right|Proven world [[oil reserves]], 2009.]]
'''Petroleum''' ([[Latin|L.]] ''petroleum'', from {{lang-gr|petra}} (rock) + ''{{lang-la|oleum}}'' (oil)<ref>"Petroleum". ''[[Concise Oxford English Dictionary]]''</ref>) or '''crude oil''' is a naturally occurring, toxic, [[flammability|flammable]] liquid consisting of a complex mixture of [[hydrocarbon]]s of various molecular weights, and other [[organic compound]]s, that are found in [[Formation (stratigraphy)|geologic formations]] beneath the [[Earth|Earth's]] surface. Petroleum is recovered mostly through [[oil drilling]]. It is refined and separated, most easily by [[boiling point]], into a large number of consumer products, from [[petrol]] and [[kerosene]] to [[asphalt]] and chemical [[reagents]] used to make [[plastics]] and [[pharmaceuticals]].<ref name="howstuff">{{cite web|url=http://www.howstuffworks.com/oil-refining.htm|title=HowStuffWorks "How Oil Refining Works"}}</ref> The term ''petroleum'' was first used in the treatise ''De Natura Fossilium'', published in 1546 by the [[Germany|German]] mineralogist [[Georg Bauer]], also known as Georgius Agricola.<ref>Bauer (1546)</ref>

==Composition==

In its strictest sense, petroleum includes only crude oil, but in common usage it includes both crude oil and [[natural gas]]. Both crude oil and natural gas are predominantly a mixture of [[hydrocarbons]]. Under surface [[standard conditions for temperature and pressure|pressure and temperature conditions]], the lighter hydrocarbons [[methane]], [[ethane]], [[propane]] and [[butane]] occur as gases, while the heavier ones from [[pentane]] and up are in the form of liquids or solids. However, in the underground [[oil reservoir]] the proportion which is gas or liquid varies depending on the subsurface conditions, and on the [[phase diagram]] of the petroleum mixture.<ref name="Hyne 2001">Hyne (2001), pp. 1–4.</ref>

An [[oil well]] produces predominantly crude oil, with some natural gas [[solubility|dissolved]] in it. Because the pressure is lower at the surface than underground, some of the gas will come out of [[solution]] and be recovered (or burned) as ''associated gas'' or ''solution gas''. A [[gas well]] produces predominately natural gas. However, because the underground temperature and pressure are higher than at the surface, the gas may contain heavier hydrocarbons such as [[pentane]], [[hexane]], and [[heptane]] in the [[gaseous state]]. Under surface conditions these will [[condense]] out of the gas and form [[natural gas condensate]], often shortened to ''condensate''. Condensate resembles [[petrol]] in appearance and is similar in composition to some [[volatility (chemistry)|volatile]] [[light crude oil]]s.

The proportion of light hydrocarbons in the petroleum mixture is highly variable between different [[oil fields]] and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils and [[bitumen]]s.

The hydrocarbons in crude oil are mostly [[alkane]]s, [[cycloalkane]]s and various [[aromatic hydrocarbon]]s while the other organic compounds contain [[nitrogen]], [[oxygen]] and [[sulfur]], and trace amounts of metals such as [[iron]], [[nickel]], [[copper]] and [[vanadium]]. The exact molecular composition varies widely from formation to formation but the proportion of [[chemical element]]s vary over fairly narrow limits as follows:<ref name="Speight">Speight (1999), p. 215–216.</ref>

{| class = "wikitable"
|+ Composition by weight
|-
! Element !! Percent range
|-
|Carbon || 83 to 87%
|-
|Hydrogen || 10 to 14%
|-
|Nitrogen || 0.1 to 2%
|-
|Oxygen || 0.1 to 1.5%
|-
|Sulfur || 0.5 to 6%
|-
|Metals || < 0.1%
|}

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.<ref name="Hyne 2001"/>

{| class = "wikitable"
|+ Composition by weight
|-
! Hydrocarbon !! Average !! Range
|-
|[[Paraffin]]s || 30% || 15 to 60%
|-
|[[Naphthene]]s || 49% || 30 to 60%
|-
|[[Aromatic]]s || 15% || 3 to 30%
|-
|[[Asphaltene|Asphaltics]] || 6% || remainder
|}

[[File:Total World Oil Reserves.PNG|thumb|250px|Most of the world's oils are non-conventional.<ref>{{cite paper|author = Alboudwarej et al.|title = Highlighting Heavy Oil|publisher = Oilfield Review|date = Summer 2006|url = http://www.slb.com/media/services/resources/oilfieldreview/ors06/sum06/heavy_oil.pdf|format = PDF|accessdate = 2008-05-24}}</ref>]]
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]] which, being heavier than most forms of crude oil, generally sinks beneath it. Crude oil may also be found in semi-solid form mixed with sand and water, as in the [[Athabasca oil sands]] in [[Canada]], where it is usually referred to as crude [[bitumen]]. In Canada, bitumen is considered a sticky, tar-like form of crude oil which is so thick and heavy that it must be heated or diluted before it will flow.<ref>{{cite web|title = Oil Sands – Glossary|work = Mines and Minerals Act|publisher = Government of Alberta|year = 2007|url = http://www.energy.gov.ab.ca/OilSands/1106.asp|archiveurl = http://web.archive.org/web/20071101112113/http://www.energy.gov.ab.ca/OilSands/1106.asp|archivedate = 2007-11-01|accessdate = 2008-10-02}}</ref> Venezuela also has large amounts of oil in the [[Orinoco oil sands]], although the hydrocarbons trapped in them are more fluid than in Canada and are usually called [[extra heavy oil]]. These oil sands resources are called [[unconventional oil]] to distinguish them from oil which can be extracted using traditional oil well methods. Between them, Canada and [[Venezuela]] contain an estimated {{convert|3.6|Toilbbl}} of bitumen and extra-heavy oil, about twice the volume of the world's reserves of conventional oil.<ref>{{cite web|title = Oil Sands in Canada and Venezuela|publisher = Infomine Inc.|year = 2008|url = http://oilsands.infomine.com/countries/|accessdate = 2008-10-02}}</ref>

Petroleum is used mostly, by volume, for producing [[fuel oil]] and [[petrol]], both important ''"[[primary energy]]"'' sources.<ref>[http://www.iea.org/bookshop/add.aspx?id=144 IEA Key World Energy Statistics]{{dead link|date=August 2010}}</ref> 84% by volume of the hydrocarbons present in petroleum is converted into energy-rich fuels (petroleum-based fuels), including petrol, diesel, jet, heating, and other fuel oils, and [[liquefied petroleum gas]].<ref>{{cite web|url=http://www.eia.doe.gov/kids/energyfacts/sources/non-renewable/oil.html#Howused |title=Crude oil is made into different fuels |publisher=Eia.doe.gov |date= |accessdate=2010-08-29}}</ref> 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]] 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]] to convert the longer, more complex molecules in the oil to the shorter, simpler ones in the fuels.

Due to its high [[energy density]], easy [[transport]]ability and [[oil reserves|relative abundance]], oil has become the world's most important source of energy since the mid-1950s. Petroleum is also the raw material for many [[chemical]] products, including [[pharmaceutical]]s, [[solvent]]s, [[fertilizer]]s, [[pesticide]]s, and [[plastic]]s; the 16% not used for energy production is converted into these other materials.
Petroleum is found in [[porosity|porous]] [[rock formations]] in the upper [[stratum|strata]] of some areas of the [[Earth]]'s [[crust (geology)|crust]]. There is also petroleum in [[tar sands|oil sands (tar sands)]]. Known [[oil reserves]] are typically estimated at around 190&nbsp;km<sup>3</sup> (1.2 [[1000000000 (number)|trillion]] [[long and short scales|(short scale)]] [[barrel (unit)|barrels]]) without oil sands,<ref>{{cite web|url=http://www.eia.doe.gov/emeu/international/reserves.html |title=EIA reserves estimates |publisher=Eia.doe.gov |date= |accessdate=2010-08-29}}</ref> or 595&nbsp;km<sup>3</sup> (3.74 trillion barrels) with oil sands.<ref>{{cite web|url=http://www.cera.com/aspx/cda/public1/news/pressReleases/pressReleaseDetails.aspx?CID=8444 |title=CERA report on total world oil |publisher=Cera.com |date=2006-11-14 |accessdate=2010-08-29}}</ref> Consumption is currently around {{convert|84|Moilbbl}} per day, or 4.9&nbsp;km<sup>3</sup> per year.

==Chemistry==
[[File:Octane molecule 3D model.png|thumb|[[Octane]], a [[hydrocarbon]] found in petroleum. Lines represent [[single bond]]s; black spheres represent [[carbon]]; white spheres represent [[hydrogen]].]]

Petroleum is a mixture of a very large number of different [[hydrocarbon]]s; the most commonly found molecules are [[alkane]]s (linear or branched), [[cycloalkane]]s, [[aromatic hydrocarbon]]s, or more complicated chemicals like [[asphaltene]]s. Each petroleum variety has a unique mix of [[molecule]]s, which define its physical and chemical properties, like color and [[viscosity]].

The ''alkanes'', also known as ''paraffins'', are [[saturation (chemistry)|saturated]] hydrocarbons with straight or branched chains which contain only [[carbon]] and [[hydrogen]] and have the general formula C<sub>n</sub>H<sub>2n+2</sub>. 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]] (C<sub>5</sub>H<sub>12</sub>) to [[octane]] (C<sub>8</sub>H<sub>18</sub>) are [[oil refinery|refined]] into [[petrol]], the ones from [[nonane]] (C<sub>9</sub>H<sub>20</sub>) to [[hexadecane]] (C<sub>16</sub>H<sub>34</sub>) into [[diesel fuel]] and [[kerosene]] (primary component of many types of [[jet fuel]]), and the ones from hexadecane upwards into [[fuel oil]] and [[lubricating oil]]. At the heavier end of the range, [[paraffin wax]] is an alkane with approximately 25 carbon atoms, while [[asphalt]] has 35 and up, although these are usually [[Fluid catalytic cracking|cracked]] 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 liquified petroleum gas under pressure, or used to power the refinery's own burners. During the winter, Butane (C<sub>4</sub>H<sub>10</sub>), is blended into the petrol pool at high rates, because butane's high vapor 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 C<sub>n</sub>H<sub>2n</sub>. Cycloalkanes have similar properties to alkanes but have higher boiling points.

The ''aromatic hydrocarbons'' are [[degree of unsaturation|unsaturated hydrocarbons]] which have one or more planar six-carbon rings called [[benzene ring]]s, to which hydrogen atoms are attached with the formula C<sub>n</sub>H<sub>n</sub>. They tend to burn with a sooty flame, and many have a sweet aroma. Some are [[carcinogenic]].

These different molecules are separated by [[fractional distillation]] at an oil refinery to produce petrol, jet fuel, kerosene, and other hydrocarbons. For example, [[2,2,4-trimethylpentane]] (isooctane), widely used in [[petrol]], has a chemical formula of C<sub>8</sub>H<sub>18</sub> and it reacts with oxygen [[exothermic]]ally:<ref>{{cite web|url=http://www.webmo.net/curriculum/heat_of_combustion/heat_of_combustion_key.html |title=Heat of Combustion of Fuels |publisher=Webmo.net |date= |accessdate=2010-08-29}}</ref>

:2 C<sub>8</sub>H<sub>18</sub>(''l'') + 25 O<sub>2</sub>(''g'') → 16 CO<sub>2</sub>(''g'') + 18 H<sub>2</sub>O(''g'') + 10.86 MJ/mol (of octane)

The amount of various molecules in an oil sample can be determined in laboratory. The molecules are typically extracted in a [[solvent]], then separated in a [[gas chromatograph]], and finally determined with a suitable [[detector]], such as a [[flame ionization detector]] or a [[mass spectrometer]].<ref>[http://www.norden.org/pub/ebook/2003-516.pdf Use of ozone depleting substances in laboratories]. TemaNord 2003:516.</ref>

Incomplete combustion of petroleum or petrol results in production of toxic byproducts. Too little oxygen results in [[carbon monoxide]]. Due to the high temperatures and high pressures involved, exhaust gases from petrol combustion in car engines usually include [[nitrogen oxide]]s which are responsible for creation of [[photochemical smog]].

==Empirical equations for the thermal properties of petroleum products==
===Heat of combustion===

At a constant volume the heat of combustion of a petroleum product can be approximated as follows:

:<math>Q_v = 12,400 - 2,100d^2</math>

where <math>Q_v</math> is measured in cal/gram and d is the specific gravity at {{convert|60|°F|°C|abbr=on}}.

===Thermal conductivity===

The thermal conductivity of petroleum based liquids can be modeled as follows:

:<math>K = \frac{0.813}{d}[1-0.0203(t-32)]</math>,

where K is measured in BTU{{middot}}hr<sup>−1</sup>ft<sup>−2</sup>&nbsp;, t is measured in °F and d is the specific gravity at {{convert|60|°F|°C|abbr=on}}.

===Specific heat===

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

:<math>c = \frac{1}{\sqrt{d}} [0.388+0.00045t]</math>,

where c is measured in BTU/lbm-°F, t is the temperature in Fahrenheit and ''d'' is the specific gravity at {{convert|60|°F|°C|abbr=on}}.

In units of kcal/(kg·°C), the formula is:

:<math>\frac{1}{\sqrt{d}} [0.402+0.00081t]</math>,

where the temperature ''t'' is in Celsius and ''d'' is the specific gravity at 15 °C.

===Latent heat of vaporization===

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

:<math>L = \frac{1}{d}[110.9 - 0.09t]</math>,

where L is measured in BTU/lbm, t is measured in °F and d is the specific gravity at {{convert|60|°F|°C|abbr=on}}.

In units of kcal/kg, the formula is:

:<math>L = \frac{1}{d}[194.4 - 0.162t]</math>,

where the temperature ''t'' is in Celsius and ''d'' is the specific gravity at 15 °C.<ref>United States Bureau of Standards, "Thermal Properties of Petroleum Products". Miscellaneous Publication No. 97, November 9th, 1929.</ref>

==Formation==
[[File:Treibs&Chlorophyll.png|thumb|350 px|right|Structure of vanadium [[porphyrin]] compound extracted from petroleum by [[Alfred E. Treibs]], father of [[organic geochemistry]]. Treibs noted the close structural similarity of this molecule and [[chlorophyll a]].]]

According to generally accepted theory, petroleum is derived from ancient [[biomass]].<ref>{{cite journal|doi=10.1016/j.orggeochem.2005.09.001|title=Organic geochemistry – A retrospective of its first 70 years☆|year=2006|last1=Kvenvolden|first1=K|journal=Organic Geochemistry|volume=37|page=1}}</ref> It is a [[fossil fuel]] derived from ancient [[fossilized]] [[organic material]]s. The theory was initially based on the isolation of molecules from petroleum that closely resemble known biomolecules.

More specifically, crude oil and [[natural gas]] are products of [[diagenesis|heating]] of ancient [[organic compound|organic materials]] (i.e. [[kerogen]]) over [[geologic time scale|geological time]]. Formation of petroleum occurs from [[hydrocarbon]] [[pyrolysis]], in a variety of mostly [[endothermic]] reactions at high temperature and/or pressure.<ref>{{cite web|url=http://www.osti.gov/bridge/servlets/purl/10169154-cT5xip/10169154.PDF |title=Petroleum Study |publisher=Osti.gov |date= |accessdate=2010-08-29}}</ref> Today's oil formed from the preserved remains of [[prehistory|prehistoric]] [[zooplankton]] and [[algae]], which had settled to a sea or lake bottom in large quantities under [[anoxic sea water|anoxic conditions]] (the remains of prehistoric [[terrestrial plant]]s, on the other hand, tended to form [[coal]]). Over geological time the organic matter mixed with [[mud]], and was buried under heavy layers of [[sediment]] resulting in high levels of [[heat]] and [[pressure]] (diagenesis). This process caused the organic matter to change, first into a waxy material known as kerogen, which is found in various [[oil shale]]s around the world, and then with more heat into liquid and gaseous hydrocarbons via a process known as [[catagenesis (geology)|catagenesis]].

There were certain warm nutrient-rich environments such as the [[Gulf of Mexico]] and the ancient [[Tethys Sea]] where the large amounts of organic material falling to the ocean floor exceeded the rate at which it could decompose. This resulted in large masses of organic material being buried under subsequent deposits such as shale formed from mud. This massive organic deposit later became heated and transformed under pressure into oil.<ref>[http://www.nytimes.com/2010/08/03/science/03oil.html "Tracing Oil Reserves to Their Tiny Origins"] article by William J. Broad in ''[[The New York Times]]'' August 2, 2010. Retrieved August 2, 2010.</ref>

Geologists often refer to the temperature range in which oil forms as an "oil window"<ref>{{cite web|url=http://oilismastery.blogspot.com/2008/05/oil-window.html |title=The "Oil Window" |publisher=Oilismastery.blogspot.com |date=2008-05-30 |accessdate=2010-08-29}}</ref>—below the minimum temperature oil remains trapped in the form of kerogen, and above the maximum temperature the oil is converted to [[natural gas]] through the process of [[thermal cracking]]. Sometimes, oil which is formed at extreme depths may migrate and become trapped at much shallower depths than where it was formed. The [[Athabasca Oil Sands]] is one example of this.

===Abiogenic origin===
{{Main|Abiogenic petroleum origin}}
A small number of geologists adhere to the [[abiogenic petroleum origin]] hypothesis and maintain that hydrocarbons of purely inorganic origin exist within Earth's interior. Chemists [[Marcellin Berthelot]] and [[Dmitri Mendeleev]], as well as astronomer [[Thomas Gold]] championed the theory in the [[Western world]] by supporting the work done by [[Nikolai Kudryavtsev]] and [[Vladimir Porfiriev]] in the 1950s. It is currently supported primarily by Jack F. Kenney, Vladilen Krayushkin, and Vladimir Kutcherov.<ref>{{cite web|url=http://www.gasresources.net/DisposalBioClaims.htm |title=Kenney et al., Dismissal of the Claims of a Biological Connection for Natural Petroleum, Energia 2001 |publisher=Gasresources.net |date= |accessdate=2010-08-29}}</ref><ref>{{cite web|url=http://www.nature.com/ngeo/journal/v2/n8/abs/ngeo591.html |title=Kolesnikov et al., Methane-Derived Hydrocarbons Produced Under Upper-Mantle Conditions, Nature, 2009 |publisher=Nature.com |date= |accessdate=2010-08-29}}</ref>

The abiogenic origin hypothesis has not yet been ruled out, but it has little support among modern [[petroleum geologist]]s.<ref>http://static.scribd.com/docs/j79lhbgbjbqrb.pdf</ref> Its advocates consider that it is "still an open question"<ref>{{cite journal| author=Anton Kolesnikov, Vladimir G. Kutcherov, Alexander F. Goncharov| title=Methane-derived hydrocarbons produced under upper-mantle conditions| journal=Nature Geoscience| volume=2| issue=8 pages=566–570| date=26 July 2009| doi=10.1038/ngeo591| page=566}}</ref> Extensive research into the chemical structure of kerogen has identified algae as the primary source of oil. The abiogenic origin hypothesis fails to explain the presence of these markers in kerogen and oil, as well as failing to explain how inorganic origin could be achieved at temperatures and pressures sufficient to convert kerogen to graphite. It has not been successfully used in uncovering oil deposits by geologists, as the hypothesis lacks any mechanism for determining where the process may occur.<ref>{{cite journal |last= Glasby|first=Geoffrey P. |year=2006 |title= Abiogenic origin of hydrocarbons: an historical overview |journal= Resource Geology|volume=56 |issue=1 |pages=83–96 |url=http://static.scribd.com/docs/j79lhbgbjbqrb.pdf |format=PDF |accessdate=2008-02-17 |doi=10.1111/j.1751-3928.2006.tb00271.x}}</ref> More recently scientists at the Carnegie Institution for Science have found that ethane and heavier hydrocarbons can be synthesized under conditions of the upper mantle.<ref>[http://www.eurekalert.org/pub_releases/2009-07/ci-hit072409.php Hydrocarbons in the deep Earth?] July 2009 (Press release)</ref>

==Crude oil==
===Crude oil reservoirs===
[[File:Structural Trap (Anticlinal).svg|thumb|140px|Hydrocarbon trap.]]
Three conditions must be present for oil reservoirs to form: a [[source rock]] rich in hydrocarbon material buried deep enough for subterranean heat to cook it into oil; a [[porous]] and [[permeability (fluid)|permeable]] reservoir rock for it to accumulate in; and a cap rock (seal) or other mechanism that prevents it 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 [[buoyancy|lighter]] than rock or water, they often migrate upward through adjacent rock layers until either reaching the surface or becoming trapped within porous rocks (known as [[oil reservoir|reservoirs]]) 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]] forms, from which the liquid can be extracted by [[drill]]ing and [[pump]]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]] plants and [[oil refineries]].

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 many reservoirs, however, eventually dissipates. Then the oil must be pumped out using “artificial lift” created by mechanical pumps powered by gas or electricity. 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% of the oil produced on a daily basis, secondary methods account for about half, and tertiary recovery the remaining 10%. 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 out the oil-saturated liquid.

===Unconventional oil reservoirs===
{{See also|Unconventional oil|Oil sands|Oil shale reserves}}
Oil-eating bacteria [[biodegradation|biodegrades]] oil that has escaped to the surface. [[Oil sands]] 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]]. These two countries have the world's largest deposits of oil sands.

On the other hand, [[oil shale]]s 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 really shales and do not really contain oil, but are usually relatively hard rocks called [[marl]]s containing a waxy substance called [[kerogen]]. The kerogen trapped 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 quantityes of pitch, tarr, and oyle out of a sort of stone." Although oil shales are found in many countries, the United States has the world's largest deposits.<ref name=Lambertson>{{cite news|title=Oil Shale: Ready to Unlock the Rock|first=Giles|last=Lambertson|publisher=Construction Equipment Guide|url=http://www.cegltd.com/story.asp?story=10092|date=2008-02-16|accessdate=2008-05-21}}</ref>

==Classification==
{{See also|Benchmark (crude oil)}}
[[File:Petroleum.JPG|thumb|A sample of medium heavy crude oil]]

The [[petroleum industry]] generally classifies crude oil by the geographic location it is produced in (e.g. [[West Texas Intermediate]], [[Brent oilfield|Brent]], or [[Oman]]), its [[API gravity]] (an oil industry measure of density), and by its sulfur content. Crude oil may be considered ''[[Light crude oil|light]]'' if it has low density or ''[[Heavy crude oil|heavy]]'' if it has high density; and it may be referred to as [[sweet crude oil|sweet]] if it contains relatively little sulfur or ''[[sour crude oil|sour]]'' 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 petrol, 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 understood by the use of [[Crude oil assay|crude oil assay analysis]] in petroleum laboratories.

[[barrel (unit)|Barrel]]s from an area in which the crude oil's molecular characteristics have been determined and the oil has been classified are used as pricing [[Benchmark (crude oil)|references]] throughout the world. Some of the common reference crudes are:

*[[West Texas Intermediate]] (WTI), a very high-quality, sweet, light oil delivered at [[Cushing, Oklahoma]] for North American oil
*[[Brent Crude|Brent Blend]], comprising 15 oils from fields in the [[Brent oilfield|Brent]] and [[Ninian]] systems in the [[East Shetland Basin]] of the [[North Sea]]. The oil is landed at [[Sullom Voe]] terminal in [[Shetland]]. Oil production from Europe, Africa and Middle Eastern oil flowing West tends to be priced off this oil, which forms a [[Benchmark (crude oil)|benchmark]]
*[[Dubai Crude|Dubai-Oman]], used as benchmark for Middle East sour crude oil flowing to the [[Asia]]-[[Pacific]] region
*[[Tapis crude|Tapis]] (from [[Malaysia]], used as a reference for light Far East oil)
*Minas (from [[Indonesia]], used as a reference for heavy Far East oil)
*The [[OPEC Reference Basket]], a weighted average of oil blends from various [[OPEC]] (The Organization of the Petroleum Exporting Countries) countries
*Midway Sunset Heavy, by which heavy oil in California is priced <ref>{{cite web|url=http://crudemarketing.chevron.com/posted_pricing_daily_california.asp |title=Chevron Crude Oil Marketing - North America Posted Pricing - California |publisher=Crudemarketing.chevron.com |date=2007-05-01 |accessdate=2010-08-29}}</ref>

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 delivered at [[Hardisty, Alberta]], and for a Brent Blend delivered at Shetland, it may be a Russian Export Blend delivered at the port of [[Primorsk, Leningrad Oblast|Primorsk]].<ref>{{cite web
|title = Light Sweet Crude Oil
|work = About the Exchange
|publisher = New York Mercantile Exchange (NYMEX)
|year = 2006
|url = http://www.nymex.com/lsco_fut_descri.aspx
|archiveurl = http://web.archive.org/web/20080314074204/http://www.nymex.com/lsco_fut_descri.aspx
|archivedate = 2008-03-14
|accessdate = 2008-04-21}}
</ref>

==Petroleum industry==
[[File:WTI price 96 09.svg|thumb|[[New York Mercantile Exchange]] prices for West Texas Intermediate 1996–2009]]
{{Main|Petroleum industry}}

The petroleum industry is involved in the global processes of [[Hydrocarbon exploration|exploration]], [[Extraction of petroleum|extraction]], [[Oil refinery|refining]], [[Petroleum transport|transporting]] (often with [[oil tanker]]s and [[Pipeline transport|pipelines]]), and marketing petroleum products. The largest volume products of the industry are [[fuel oil]] and [[petrol]] . Petroleum is also the raw material for many [[Petrochemical|chemical products]], including pharmaceuticals, solvents, fertilizers, pesticides, and plastics. The industry is usually divided into three major components: [[Upstream (oil industry)|upstream]], [[midstream]] and [[Downstream (oil industry)|downstream]]. Midstream operations are usually included in the downstream category.

Petroleum is vital to many [[industries]], and is of importance to the maintenance of industrialized [[civilization]] itself, and thus is critical concern to many nations. Oil accounts for a large percentage of the world's energy consumption, ranging from a low of 32% for [[Europe]] and Asia, up to a high of 53% for the [[Middle East]]. Other geographic regions' consumption patterns are as follows: South and [[Central America]] (44%), [[Africa]] (41%), and [[North America]] (40%). The world at large consumes 30 billion [[Barrel (unit)|barrels]] (4.8&nbsp;km³) of oil per year, and the top oil consumers largely consist of developed nations. In fact, 24% of the oil consumed in 2004 went to the [[United States]] alone,<ref>{{cite web
|title=International Energy Annual 2004
|publisher=Energy Information Administration
|date=2006-07-14
|url=http://www.eia.doe.gov/pub/international/iealf/tablee2.xls
|format=XLS}}<!-- For annual updates use the search at http://www.eia.doe.gov/ for terms "International Energy Annual 2006" "Tables" "Petroleum consumption" --></ref> though by 2007 this had dropped to 21% of world oil consumed.<ref>{{cite web
|title=Yearbook 2008 - crude oil
|publisher=Energy data
|url=http://yearbook.enerdata.net}}
</ref>

In the US, in the states of [[Arizona]], [[California]], [[Hawaii]], [[Nevada]], [[Oregon]] and [[Washington (U.S. state)|Washington]], the [[Western States Petroleum Association]] (WSPA) represents companies responsible for producing, distributing, refining, transporting and marketing petroleum. This non-profit trade association was founded in 1907, and is the oldest petroleum trade association in the United States.<ref>
{{cite web
|url=http://www.wspa.org/about/index.htm
|title=Western States Petroleum Association - About Us
|accessdate=2008-11-03
|archiveurl = http://web.archive.org/web/20080616140609/http://www.wspa.org/about/index.htm |archivedate = June 16, 2008}}</ref>

==History==
{{Main|History of petroleum}}
[[File:Gusher Okemah OK 1922.jpg|thumb|Oil derrick in [[Okemah, Oklahoma]], 1922.]]
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 mostly due to the invention of the [[internal combustion engine]], the rise in [[commercial aviation]] and the increasing use of [[plastic]].

More than 4000 years ago, according to [[Herodotus]] and [[Diodorus Siculus]], [[asphalt]] was used in the construction of the walls and towers of [[Babylon]]; there were oil pits near [[Ardericca]] (near Babylon), and a pitch spring on [[Zacynthus]].<ref name=EB1911>{{1911|article=Petroleum}}</ref> Great quantities of it were found on the banks of the river [[Issus (river)|Issus]], one of the tributaries of the [[Euphrates]]. Ancient [[Persian Empire|Persian]] tablets indicate the medicinal and lighting uses of petroleum in the upper levels of their society.

In the 1850s, the process to distill kerosene from petroleum was invented by [[Ignacy Łukasiewicz]], providing a cheaper alternative to [[whale oil]]. The demand for the petroleum as a fuel for lighting in North America and around the world quickly grew.<ref>Maugeri (2006), p. 3</ref> The world's first commercial oil well was drilled in [[Poland]] in 1853. Oil exploration developed in many parts of the world with the Russian Empire, particularly the [[Branobel]] company in [[Azerbaijan]], taking the lead in production by the end of the 19th century.<ref name = "Akiner">Akiner(2004), p. 5</ref> Oil exploration in North America during the early 20th century later led to the U.S. becoming the leading producer by the mid 1900s. As petroleum production in the U.S. peaked during the 1960s, however, Saudi Arabia and Russia surpassed the U.S.

Today, about 90% of vehicular fuel needs are met by oil. Petroleum also makes up 40% of total energy consumption in the [[United States]], but is responsible for only 2% 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 [[commodity|commodities]].

The top three oil producing countries are [[Saudi Arabia]], [[Russia]], and the [[United States]].<ref>{{cite web|url=http://www.infoplease.com/ipa/A0922041.html |title=InfoPlease |publisher=InfoPlease |date= |accessdate=2010-08-29}}</ref> About 80% of the world's readily accessible reserves are located in the [[Middle East]], with 62.5% coming from the Arab 5: [[Saudi Arabia]], [[UAE]], [[Iraq]], [[Qatar]] and [[Kuwait]]. A large portion of the world's total oil exists as unconventional sources, such as [[bitumen]] in [[Athabasca oil sands|Canada]] and [[Orinoco Belt|Venezuela]] and [[oil shale]]. 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.

==Price==
{{Main|Price of petroleum}}
After the collapse of the OPEC-administered pricing system in 1985, and a short lived experiment with netback pricing, oil-exporting countries adopted a market-linked pricing mechanism.<ref name="Mabro">Mabro (2006), p. 351.</ref> First adopted by [[PEMEX]] in 1986, market-linked pricing was widely accepted, and by 1988 became and still is the main method for pricing crude oil in international trade.<ref name="Mabro" /> The current reference, or pricing markers, are [[Brent Crude|Brent]], [[West Texas Intermediate|WTI]], and [[Dubai Crude|Dubai/Oman]].<ref name="Mabro" />

==Uses==
{{See|Petroleum products}}
The chemical structure of petroleum is [[Heterogeneity|heterogeneous]], composed of [[hydrocarbon]] chains of different lengths. Because of this, petroleum may be taken to [[oil refinery|oil refineries]] and the hydrocarbon chemicals separated by [[distillation]] and treated by other [[chemical process]]es, to be used for a variety of purposes. See [[Petroleum product]]s.

===Fuels===
The most common [[Petroleum distillation|distillation]]s of petroleum are [[fuel]]s.
Fuels include (by increasing molecular masses):

*[[Liquefied petroleum gas]] (LPG)
*[[Ethane]] and other short-chain [[alkanes]]
*[[Gasoline]] (Petrol)
*[[Diesel fuel]] (petrodiesel)
*[[Kerosene]]
*[[Jet fuel]]
*[[Fuel oil]]s

===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
*[[Lubricant]]s (produces light machine oils, [[motor oil]]s, and [[Grease (lubricant)|grease]]s, adding [[viscosity]] stabilizers as required).
*[[Wax]], used in the packaging of [[frozen food]]s, among others.
*[[Sulfur]] or [[Sulfuric acid]]. These are a 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]]s to be used as precursors in other [[chemical]] production.

==Petroleum by country==
<!-- this was a left over from a previous incarnation of the section. It is no longer a useful link. I looked around for a better link but didn't find one. Feel free to create an article on consumption/production etc. by country {{main|Petroleum Industry}} -->

===Consumption statistics===
<gallery widths=160px heights=140px>
File:Global Carbon Emissions.svg|Global fossil carbon emissions, an indicator of consumption, for 1800–2007. Total is black, Oil is in blue.
File:EIA_IEO2006.jpg|World energy consumption, 1980–2030. ''Source: International Energy Outlook 2006.''
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: <font style="color:red">'''red'''</font>=USA, <font style="color:blue">'''blue'''</font>=Europe, <font style="color:#D1D117">'''yellow'''</font>=Asia+Oceania
</gallery>

===Consumption===
<!-- Image with unknown copyright status removed: [[File:WorldPetroleum2007.png|thumb|center|550px|Mean oil production by country in 2007, shown as a percentage of the top producer (Saudi Arabia – 10.2 millions of barrels per day).]] -->
[[File:OilConsumptionpercapita.png|thumb|center|550px|Oil consumption per capita (darker colors represent more consumption).]]

This table orders the amount of petroleum consumed in 2008 in thousand [[Barrel (unit)|barrels]] (bbl) per day and in thousand [[cubic metre]]s (m<sup>3</sup>) per day:<ref>U.S. Energy Information Administration. [http://www.eia.doe.gov/emeu/international/RecentPetroleumConsumptionBarrelsperDay.xls Excel file] from [http://tonto.eia.doe.gov/dnav/pet/pet_pri_wco_k_w.htm this] web page. Table Posted: March 1, 2010</ref><ref>From DSW-Datareport 2008 ("Deutsche Stiftung Weltbevölkerung")</ref><ref>One cubic metre of oil is equivalent to 6.28981077 barrels of oil</ref>
{| style="text-align:right;" class="wikitable sortable"
|-
!Consuming Nation 2008
!(1000 bbl/day)
!(1000 m<sup>3</sup>/day)
!population in millions
!bbl/year per capita
|-
|{{rh}}|[[United States]] <sup>1</sup> || {{convert|19497.95|oilbbl|m3|1|disp=table}} || 314
|{{round|{{#expr:365*19497.95/314658}}|1}}
|-
|{{rh}}|[[China]] || {{convert|7831.00|oilbbl|m3|1|disp=table}} || 1345
|{{round|{{#expr:365*7831.00/1345750}}|1}}
|-
|{{rh}}|[[Japan]] <sup>2</sup> || {{convert|4784.85|oilbbl|m3|1|disp=table}} || 127
|{{round|{{#expr:365*4784.85/127156}}|1}}
|-
|{{rh}}|[[India]] <sup>2</sup> || {{convert|2962.00|oilbbl|m3|1|disp=table}} || 1198
|{{round|{{#expr:365*2962.00/1198003}}|1}}
|-
|{{rh}}|[[Russia]] <sup>1</sup> || {{convert|2916.00|oilbbl|m3|1|disp=table}} || 140
|{{round|{{#expr:365*2916.00/140873}}|1}}
|-
|{{rh}}|[[Germany]] <sup>2</sup> || {{convert|2569.28|oilbbl|m3|1|disp=table}} || 82
|{{round|{{#expr:365*2569.28/82166}}|1}}
|-
|{{rh}}|[[Brazil]] || {{convert|2485.00|oilbbl|1|m3|1|disp=table}} || 193
|{{round|{{#expr:365*2485.00/193733}}|1}}
|-
|{{rh}}|[[Saudi Arabia]] ([[OPEC]]) || {{convert|2376.00|oilbbl|1|m3|1|disp=table}} || 25
|{{round|{{#expr:365*2376.00/25720}}|1}}
|-
|{{rh}}|[[Canada]] || {{convert|2261.36|oilbbl|1|m3|1|disp=table}} || 33
|{{round|{{#expr:365*2261.36/33573}}|1}}
|-
|{{rh}}|[[South Korea]] <sup>2</sup> || {{convert|2174.91|oilbbl|1|m3|1|disp=table}} || 48
|{{round|{{#expr:365*2174.91/48332}}|1}}
|-
|{{rh}}|[[Mexico]] <sup>1</sup> || {{convert|2128.46|oilbbl|1|m3|1|disp=table}} || 109
|{{round|{{#expr:365*2128.46/109610}}|1}}
|-
|{{rh}}|[[France]] <sup>2</sup>|| {{convert|1986.26|oilbbl|1|m3|1|disp=table}} || 62
|{{round|{{#expr:365*1986.26/62342}}|1}}
|-
|{{rh}}|[[Iran]] ([[OPEC]])|| {{convert|1741.00|oilbbl|1|m3|1|disp=table}} || 74
|{{round|{{#expr:365*1741.00/74195}}|1}}
|-
|{{rh}}|[[United Kingdom]] <sup>1</sup> || {{convert|1709.66|oilbbl|1|m3|1|disp=table}} || 61
|{{round|{{#expr:365*1709.66/61565}}|1}}
|-
|{{rh}}|[[Italy]] <sup>2</sup>|| {{convert|1639.01|oilbbl|1|m3|1|disp=table}} || 60
|{{round|{{#expr:365*1639.01/59870}}|1}}
|}
Source: [http://www.eia.doe.gov/emeu/cabs/topworldtables1_2.htm US Energy Information Administration]

Population Data:<ref>{{cite web|url=http://www.ibge.gov.br/paisesat/main.php |title=IBGE |publisher=IBGE |date= |accessdate=2010-08-29}}</ref>

<small><sup>1</sup> [[Peak oil|peak production of oil]] already passed in this state</small>

<small><sup>2</sup> This country is not a major oil producer</small>

===Production===
{{For|oil reserves by country|Oil reserves#Proven reserves in order}}

[[File:Oil producing countries map.png|thumb|center|550px|Oil producing [[List of oil-producing states|countries]]]]

[[File:Top Oil Producing Counties.png|thumb|250px|right|Graph of Top Oil Producing Countries 1960–2006, including Soviet Union<ref>{{cite web|url=http://www.eia.doe.gov/emeu/aer/pdf/pages/sec11_10.pdf |title=World Crude Oil Production |format=PDF |date= |accessdate=2010-08-29}}</ref>]]

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

{| style="text-align:right;" class="wikitable sortable"
|-
!#
!Producing Nation
!10<sup>3</sup>bbl/d (2006)
!10<sup>3</sup>bbl/d (2007)
!10<sup>3</sup>bbl/d (2008)
|-
|1
|{{rh}}|[[Saudi Arabia]] ([[OPEC]])
|10,665
|10,234
|10,782
|-
|2
|{{rh}}|[[Russia]] <sup>1</sup>
|9,677
|9,876
|9,789
|-
|3
|{{rh}}|[[United States]] <sup>1</sup>
|8,331
|8,481
|8,514
|-
|4
|{{rh}}|[[Iran]] (OPEC)
|4,148
|4,043
|4,174
|-
|5
|{{rh}}|[[China]]
|3,845
|3,901
|3,973
|-
|6
|{{rh}}|[[Canada]] <sup>2</sup>
|3,288
|3,358
|3,350
|-
|7
|{{rh}}|[[Mexico]] <sup>1</sup>
|3,707
|3,501
|3,185
|-
|8
|{{rh}}|[[United Arab Emirates]] (OPEC)
|2,945
|2,948
|3,046
|-
|9
|{{rh}}|[[Kuwait]] (OPEC)
|2,675
|2,613
|2,742
|-
|10
|{{rh}}|[[Venezuela]] (OPEC) <sup>1</sup>
|2,803
|2,667
|2,643
|-
|11
|{{rh}}|[[Norway]] <sup>1</sup>
|2,786
|2,565
|2,466
|-
|12
|{{rh}}|[[Brazil]]
|2,166
|2,279
|2,401
|-
|13
|{{rh}}|[[Iraq]] (OPEC) <sup>3</sup>
|2,008
|2,094
|2,385
|-
|14
|{{rh}}|[[Algeria]] (OPEC)
|2,122
|2,173
|2,179
|-
|15
|{{rh}}|[[Nigeria]] (OPEC)
|2,443
|2,352
|2,169
|-
|16
|{{rh}}|[[Angola]] (OPEC)
|1,435
|1,769
|2,014
|-
|17
|{{rh}}|[[Libya]] (OPEC)
|1,809
|1,845
|1,875
|-
|18
|{{rh}}|[[United Kingdom]]
|1,689
|1,690
|1,584
|-
|19
|{{rh}}|[[Kazakhstan]]
|1,388
|1,445
|1,429
|-
|20
|{{rh}}|[[Qatar]] (OPEC)
|1,141
|1,136
|1,207
|-
|21
|{{rh}}|[[Indonesia]]
|1,102
|1,044
|1,051
|-
|22
|{{rh}}|[[India]]
|854
|881
|884
|-
|23
|{{rh}}|[[Azerbaijan]]
|648
|850
|875
|-
|24
|{{rh}}|[[Argentina]]
|802
|791
|792
|-
|25
|{{rh}}|[[Oman]]
|743
|714
|761
|-
|26
|{{rh}}|[[Malaysia]]
|729
|703
|727
|-
|27
|{{rh}}|[[Egypt]]
|667
|664
|631
|-
|28
|{{rh}}|[[Colombia]]
|544
|543
|601
|-
|29
|{{rh}}|[[Australia]]
|552
|595
|586
|-
|30
|{{rh}}|[[Ecuador]] (OPEC)
|536
|512
|505
|-
|31
|{{rh}}|[[Sudan]]
|380
|466
|480
|-
|32
|{{rh}}|[[Syria]]
|449
|446
|426
|-
|33
|{{rh}}|[[Equatorial Guinea]]
|386
|400
|359
|-
|34
|{{rh}}|[[Thailand]]
|334
|349
|361
|-
|35
|{{rh}}|[[Vietnam]]
|362
|352
|314
|-
|36
|{{rh}}|[[Yemen]]
|377
|361
|300
|-
|37
|{{rh}}|[[Denmark]]
|344
|314
|289
|-
|38
|{{rh}}|[[Gabon]]
|237
|244
|248
|-
|39
|{{rh}}|[[South Africa]]
|204
|199
|195
|-
|40
|{{rh}}|[[Turkmenistan]]
|No data
|180
|189
|}
Source: [http://tonto.eia.doe.gov/country/index.cfm U.S. Energy Information Administration]

<small><sup>1</sup> Peak production of conventional oil already passed in this state</small>

<small><sup>2</sup> Although Canadian conventional oil production is declining, total oil production is increasing as oil sands production grows. If oil sands are included, it has the world's second largest oil reserves after Saudi Arabia.

<small><sup>3</sup> Though still a member, Iraq has not been included in production figures since 1998</small>

===Export===
{{See also|Fossil fuel exporters}}
[[File:Oil exports.PNG|thumb|550px|right|Oil exports by country.]]

In order of net exports in 2006 in thousand [[Barrel (unit)|bbl]]/[[Day|d]] and thousand [[Cubic metre|m³]]/d:
{| style="text-align:right;" class="wikitable sortable"
|-
!#
!Exporting Nation (2006)
!(10<sup>3</sup>bbl/d)
!(10<sup>3</sup>m<sup>3</sup>/d)
|-
|1
|{{rh}}|[[Saudi Arabia]] ([[OPEC]])
|8,651
|1,376
|-
|2
|{{rh}}|[[Russia]] <sup>1</sup>
|6,565
|1,044
|-
|3
|{{rh}}|[[Norway]] <sup>1</sup>
|2,542
|404
|-
|4
|{{rh}}|[[Iran]] (OPEC)
|2,519
|401
|-
|5
|{{rh}}|[[United Arab Emirates]] (OPEC)
|2,515
|400
|-
|6
|{{rh}}|[[Venezuela]] (OPEC) <sup>1</sup>
|2,203
|350
|-
|7
|{{rh}}|[[Kuwait]] (OPEC)
|2,150
|342
|-
|8
|{{rh}}|[[Nigeria]] (OPEC)
|2,146
|341
|-
|9
|{{rh}}|[[Algeria]] (OPEC) <sup>1</sup>
|1,847
|297
|-
|10
|{{rh}}|[[Mexico]] <sup>1</sup>
|1,676
|266
|-
|11
|{{rh}}|[[Libya]] (OPEC) <sup>1</sup>
|1,525
|242
|-
|12
|{{rh}}|[[Iraq]] (OPEC)
|1,438
|229
|-
|13
|{{rh}}|[[Angola]] (OPEC)
|1,363
|217
|-
|14
|{{rh}}|[[Kazakhstan]]
|1,114
|177
|-
|15
|{{rh}}|[[Canada]] <sup>2</sup>
|1,071
|170
|}
Source: [http://www.eia.doe.gov/emeu/cabs/topworldtables1_2.htm US Energy Information Administration]

<small><sup>1</sup> [[Peak oil|peak production]] already passed in this state</small>

<small><sup>2</sup> 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 2.5 MMbbl/d in August 2007.
[http://tonto.eia.doe.gov/dnav/pet/pet_move_impcus_a2_nus_ep00_im0_mbblpd_m.htm].</small>

Total world production/consumption (as of 2005) is approximately {{convert|84|Moilbbl/d|m3/d}}.

{{See also|Organization of Petroleum Exporting Countries}}

===Import===
[[File:Oil imports.PNG|thumb|550px|right|Oil imports by country.]]

In order of net imports in 2006 in thousand [[Barrel (unit)|bbl]]/[[Day|d]] and thousand [[Cubic metre|m³]]/d:
{| style="text-align:right;" class="wikitable sortable"
|-
!#
!Importing Nation (2006)
!(10<sup>3</sup>bbl/day)
!(10<sup>3</sup>m<sup>3</sup>/day)
|-
|1
|{{rh}}|United States <sup>1</sup>
|12,220
|1,943
|-
|2
|{{rh}}|Japan
|5,097
|810
|-
|3
|{{rh}}|China <sup>2</sup>
|3,438
|547
|-
|4
|{{rh}}|Germany
|2,483
|395
|-
|5
|{{rh}}|South Korea
|2,150
|342
|-
|6
|{{rh}}|France
|1,893
|301
|-
|7
|{{rh}}|India
|1,687
|268
|-
|8
|{{rh}}|Italy
|1,558
|248
|-
|9
|{{rh}}|Spain
|1,555
|247
|-
|10
|{{rh}}|Republic of China (Taiwan)
|942
|150
|-
|11
|{{rh}}|Netherlands
|936
|149
|-
|12
|{{rh}}|Singapore
|787
|125
|-
|13
|{{rh}}|Thailand
|606
|96
|-
|14
|{{rh}}|Turkey
|576
|92
|-
|15
|{{rh}}|Belgium
|546
|87
|}
Source: [http://www.eia.doe.gov/emeu/cabs/topworldtables1_2.htm US Energy Information Administration]{{verification failed|date=July 2010|reason=maybe doe.gov changed? suggest clarify this table by using WebCite to save a snapshot from a specific year}}

<small><sup>1</sup> [[Peak oil|peak production of oil]] already passed in this state</small>

<small><sup>2</sup> Major oil producer whose production is still increasing</small>

===Non-producing consumers===
Countries whose oil production is 10% or less of their consumption.

{| style="text-align:right;" class="wikitable sortable"
|-
!#
!Consuming Nation
!(bbl/day)
!(m³/day)
|-
|1
|{{rh}}|Japan
|5,578,000
|886,831
|-
|2
|{{rh}}|Germany
|2,677,000
|425,609
|-
|3
|{{rh}}|South Korea
|2,061,000
|327,673
|-
|4
|{{rh}}|France
|2,060,000
|327,514
|-
|5
|{{rh}}|Italy
|1,874,000
|297,942
|-
|6
|{{rh}}|Spain
|1,537,000
|244,363
|-
|7
|{{rh}}|Netherlands
|946,700
|150,513
|-
|8
|{{rh}}|Turkey
|575,011
|91,663
|}
Source: [https://www.cia.gov/library/publications/the-world-factbook/rankorder/2175rank.html CIA World Factbook]{{verification failed|date=July 2010|reason=maybe factbook changed? suggest clarify this table by using a factbook snapshot of a specific year}}

==Environmental effects==
[[File:Dieselrainbow.jpg|thumb|Diesel fuel spill on a road]]
{{Main|Environmental issues with petroleum}}

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 (like [[seismology|seismic]] exploration, [[Boring (earth)|drilling]], extraction, refining and combustion). Phenomena such as [[petroleum seep|seeps]]<ref>http://seeps.wr.usgs.gov/ Natural Oil and Gas Seeps in California</ref> and [[tar pit]]s are examples of areas that petroleum naturally affects. Regardless of source, petroleum's effects when released into the environment are similar.

===Extraction===
Oil extraction is simply the removal of oil from the reservoir (oil pool). Oil extraction is costly and sometimes environmentally damaging, although [[John Hunt (oceanographer)|Dr. John Hunt]] of the [[Woods Hole Oceanographic Institution]] pointed out in a 1981 paper that over 70% of the reserves in the world are associated with visible [[seep|macroseepage]]s, and many oil fields are found due to natural [[seep]]s. Offshore exploration and extraction of oil disturbs the surrounding marine environment.<ref>[http://www.offshore-environment.com/discharges.html Waste discharges during the offshore oil and gas activity] by Stanislave Patin, tr. Elena Cascio</ref>

===Oil spills===
{{Main|Oil spill}}
[[File:PrestigeVolunteersInGaliciaCoast.jpg|thumb|Volunteers cleaning up the aftermath of the [[Prestige oil spill]]]]

Crude oil and refined fuel [[Oil spill|spills]] from [[tanker (ship)|tanker ship]] accidents have damaged natural [[ecosystem]]s in [[Alaska]], the [[Gulf of Mexico]] the [[Galapagos 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., [[Atlantic Empress]], [[Amoco Cadiz]]). Smaller spills have already proven to have a great impact on ecosystems, such as the [[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 mile]]s in a thin [[oil slick]] which can cover [[beach]]es 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 [[Torrey Canyon]] wreck produced poor results;<ref>[[Torrey Canyon#Accident|Torrey Canyon bombing by the Navy and RAF]]</ref> modern techniques would include pumping the oil from the wreck, like in the [[Prestige oil spill]] or the [[Erika (tanker)|Erika]] oil spill.<ref>{{cite web|url=http://www.total.com/en/group/news/special_report_erika/erika_measures_total/erika_pumping_cargo_11379.htm |title=Pumping of the Erika cargo |publisher=Total.com |date= |accessdate=2010-08-29}}</ref>

Though crude oil is predominantly composed of various hydrocarbons, certain nitrogen heterocylic 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 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]] and have been shown to degrade these contaminants.<ref>Sims, G. K. and E.J. O'Loughlin. 1989. Degradation of pyridines in the environment. CRC Critical Reviews in Environmental Control. 19(4): 309-340.</ref>

===Tarballs===

A tarball is a blob of [[crude oil|oil]] (not to be confused with [[tar]], which is typically derived from pine trees rather than 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.<ref name=itah>A. Y. Itah and J. P. Essien, Growth Profile and Hydrocarbonoclastic Potential of Microorganisms Isolated from Tarballs in the Bight of Bonny, Nigeria, ''World Journal of Microbiology and Biotechnology'', Volume 21, Numbers 6-7, October, 2005, doi 10.1007/s11274-004-6694-z, p 1317-1322</ref><ref name="hostettler">Frances D. Hostettler, Robert J. Rosenbauer, Thomas D. Lorenson, Jennifer Dougherty, Geochemical characterization of tarballs on beaches along the California coast. Part I-- Shallow seepage impacting the Santa Barbara Channel Islands, Santa Cruz, Santa Rosa and San Miguel, Organic Geochemistry, Volume 35, Issue 6, June 2004, Pages 725-746, ISSN 0146-6380, DOI: 10.1016/j.orggeochem.2004.01.022. [http://www.sciencedirect.com/science/article/B6V7P-4C47JKF-3/2/138e858a8f538caf6c2a0482290c3e1f]</ref> 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,<ref>Anthony H Knap, Kathryn A Burns, Rodger Dawson, Manfred Ehrhardt and Karsten H Palmork, Dissolved/dispersed hydrocarbons, tarballs and the surface microlayer: Experiences from an IOC/UNEP Workshop in Bermuda, December, 1984, ''Marine Pollution Bulletin'', Volume 17, Issue 7, July 1986, Pages 313-319. doi:10.1016/0025-326X(86)90217-1</ref><ref>Zhendi Wang, Merv Fingas, Michael Landriault, Lise Sigouin, Bill Castle, David Hostetter, Dachung Zhang, Brad Spencer, Identification and Linkage of Tarballs from the Coasts of Vancouver Island and Northern California Using GC/MS and Isotopic Techniques, ''Journal of High Resolution Chromatography'', Volume 21 Issue 7, Pages 383 - 395, doi:10.1002/(SICI)1521-4168(19980701)21:7<383::AID-JHRC383>3.0.CO;2-3</ref> and tarballs themselves may be dispersed over long distances by deep sea currents.<ref name="hostettler" /> They are slowly decomposed by bacteria, including ''[[Chromobacterium violaceum]]'', ''[[Cladosporium resinae]]'', ''[[Bacillus submarinus]]'', ''[[Micrococcus varians]]'', ''[[Pseudomonas aeruginosa]]'', ''[[Candida marina]]'' and ''[[Saccharomyces estuari]]''.<ref name=itah />

===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]].<ref>[http://www.littletechshoppe.com/ns1625/gesner.html How Capitalism Saved the Whales] by James S. Robbins, ''The Freeman'', August, 1992.</ref>

==Alternatives to petroleum==
{{See|Renewable energy}}

In the United States in 2007 about 70% of petroleum was used for transportation (e.g. petrol, diesel, jet fuel), 24% by industry (e.g. production of plastics), 5% for residential and commercial uses, and 2% for electricity production.<ref>[http://www.eia.doe.gov/emeu/aer/pecss_diagram.html "U.S. Primary Energy Consumption by Source and Sector, 2007"]. Energy Information Administration</ref> Outside of the US, a higher proportion of petroleum tends to be used for electricity.<ref>[http://www.google.com/url?sa=t&ct=res&cd=9&url=http%3A%2F%2Fwww.rrcap.unep.org%2Fmd%2Fmalereport%2F2006%2FProceeding%2FII_RCS3%2FAtt5_Initiatives%2FRSC3_2-5_Power%2520Sector%2520.ppt&ei=2rd1SPrQJZGqtQPhoqTaCg&usg=AFQjCNH7BuzJZE0sFU7RB8cQOgOdC_I7EA&sig2=FINHJAE_jFS-2O7y1u8uvQ needtitle] UN Energy Program</ref>

===Alternatives to petroleum-based vehicle fuels===
{{Main|Alternative propulsion|Biofuel|Hydrogen economy}}

Alternative propulsion refers to both:
*[[Alternative fuel]]s used in standard or modified [[internal combustion engine]]s (i.e. [[biofuel]]s or [[Hydrogen vehicle#Hydrogen|combustion hydrogen]]).
*propulsion systems not based on internal combustion, such as those based on [[electricity]] (for example, [[electric vehicle|all-electric]] or [[hybrid vehicle]]s), [[air vehicle|compressed air]], or [[fuel cell]]s (i.e. [[hydrogen vehicle#Fuel cell|hydrogen fuel cells]]).

Currently, cars can be classified into the following groups:
*[[Internal combustion engine]] cars, which may use
**petrol, fuel and/or biofuels (e.g. alcohol, [[biodiesel]] and [[biobutanol]])
**[[compressed natural gas]] used by [[natural gas vehicle]]s
**[[hydrogen]] in [[hydrogen vehicle]]s.

*Advanced technology cars such as [[hybrid vehicle]]s which use petroleum and/or biofuels, albeit far more efficiently.<ref>Amory B. Lovins,
E. Kyle Datta, Odd-Even Bustnes, Jonathan G. Koomey, Nathan J. Glasgow. [http://www.oilendgame.com/pdfs/WtOEg_ExecSummary.pdf "Winning the oil endgame"] Rocky Mountain Institute</ref>
*[[Plug-in hybrid]]s, that can store and use externally produced electricity in addition to petroleum.
*[[electric car]]s

===Alternatives to using oil in industry===
{{Expand|date=July 2008}}
Biological feedstocks do exist for industrial uses such as plastic production.<ref>[http://seattletimes.nwsource.com/html/businesstechnology/2003646852_bioprocessing02.html Bioprocessing] ''Seattle Times'' (2003)</ref>

===Alternatives to burning petroleum for electricity===
{{Main|Alternative energy|Nuclear power|Renewable energy}}
In oil producing countries with little refinery capacity, oil is sometimes burned to produce electricity. [[Renewable energy]] technologies such as [[solar power]], [[wind power]], [[micro hydro]], [[biomass]] and [[biofuels]] might someday be used to replace some of these generators, but today the primary alternatives remain large scale [[hydroelectricity]], [[nuclear power|nuclear]] and [[coal]]-fired generation.

==Future of petroleum production==
Consumption in the twentieth century has been abundantly pushed by automobile growth; the [[1980s oil glut|1985-2003 oil glut]] even fuelled the sales of low economy vehicles (SUVs) in [[OECD]] countries. In 2008, the economic crisis seems to have some impact on the sales of such vehicles; still, the 2008 oil consumption shows a small increase. The [[BRIC]] countries might also kick in, as China briefly was the first automobile market in December 2009.<ref name=China-market>
{{cite news
|url=http://news.bbc.co.uk/2/hi/business/7879372.stm
|title=China's car industry overtakes US
|author=Chris Hogg
|date=2009-02-10
| work=BBC News
}}</ref> The immediate outlook still hints upwards.
In the long term, uncertainties linger; the [[OPEC]] believes that the [[OECD]] countries will push low consumption policies at some point in the future; when that happens, it will definitely curb the oil sales, and both [[OPEC]] and [[Energy Information Administration|EIA]] kept lowering their 2020 consumption estimates during the past 5 years.<ref name="OPEC-Publications, fig 1.19 P48">
{{cite web
|url=http://www.opec.org/library/World%20Oil%20Outlook/pdf/WOO2008.pdf
|title=World Oil Outlook 2008
|author=OPEC Secretariat
|year=2008
}}{{dead link|date=August 2010}}</ref> Oil products are more and more in competition with alternative sources, mainly coal and natural gas, both cheaper sources.

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 <ref name=DaQing>
{{cite web
|url=http://en.ce.cn/Insight/200610/16/t20061016_8980162.shtml
|title=Daqing Oilfield rejuvenated by virtue of technology
|author=Ni Weiling
|date=2006-10-16
}}</ref> ) will continue to play a major role in increasing the world's recoverable oil.

===Hubbert peak theory===
{{Main|Peak oil|Hubbert peak theory}}
The Hubbert peak theory (also known as peak oil) posits 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.<ref name=campbell1222000>
{{cite web
|url=http://energycrisis.org/de/lecture.html
|title=Peak Oil Presentation at the Technical University of Clausthal
|author=Campbell CJ
|date=2000-12
}}</ref>

Controversy surrounds predictions of the timing of the global peak, as these predictions are dependent on the past production and discovery data used in the calculation as well as how unconventional reserves are considered.{{Citation needed|date=November 2009}} Also, these predictions do not take into account outside elements such as the current economic crisis (2008).{{Citation needed|date=November 2009}} Also, many Peak Oil promoters proposed many different dates, some of them passed already.{{Citation needed|date=November 2009}} Despite these uncertainties, Hubbert applied his theory to predict the peak of U.S. oil production at a date between 1966 and 1970. This prediction was based on data available at the time of his publication in 1956. In the same paper, Hubbert predicts the world Peak Oil for the year 2000.<ref name=hubbert03091956>
{{cite journal
|url=http://www.hubbertpeak.com/Hubbert/1956/1956.pdf
|last1=Hubbert |first1=Marion King
|last2=Shell Development Company
|title=Nuclear energy and the fossil fuels
|journal=Drilling and Production Practice
|volume=95
|publisher=American Petroleum Institute
|location=Washington, DC
|year=1956
}}</ref>

It is difficult to predict the [[peak oil|oil peak]] in any given region, due to the lack of knowledge and/or transparency in [[accounting]] of global oil reserves.<ref>{{cite web|url=http://www.iags.org/n0331043.htm |title=New study raises doubts about Saudi oil reserves |publisher=Iags.org |date=2004-03-31 |accessdate=2010-08-29}}</ref> 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.

Since virtually all economic sectors rely heavily on petroleum, peak oil could lead to a "partial or complete failure of markets," says one study.<ref>"[http://www.spiegel.de/international/germany/0,1518,715138,00.html Military Study Warns of a Potentially Drastic Oil Crisis]". ''[[Der Spiegel|Spiegel Online]]''. September 1, 2010.</ref>

==See also==
{{Portal|Energy}}
{{Wikinewscat|Energy}}
*[[Barrel of oil equivalent]]
*[[Gas oil ratio]]
*[[List of countries by proven oil reserves]]
*[[List of oil fields]]
*[[List of petroleum companies]]
*[[Manure-derived synthetic crude oil]]
*[[Oil burden]]
*[[Petroleum geology]]
*[[Thermal depolymerization]]
*[[Waste oil]]

==Notes==
<!-- No longer referenced: #{{note|Kenney2002}} {{cite journal|author=Kenney, J., Kutcherov, V., Bendeliani, N. and Alekseev, V.|title= The evolution of multicomponent systems at high pressures: VI. The thermodynamic stability of the hydrogen–carbon system: The genesis of hydrocarbons and the origin of petroleum|journal=Proceedings of the National Academy of Sciences of the U.S.A.|volume=99|year=2002|pages=10976–10981|doi = 10.1073/pnas.172376899|pmid= 12177438|issue=17|pmc=123195}}-->
{{Reflist|colwidth=30em}}

==References==
*{{cite book|editor=Akiner, Shirin; Aldis, Anne|title=The Caspian: Politics, Energy and Security|publisher=Routledge|year=2004|location=New York|isbn=978-0-7007-0501-6}}
*{{cite book |authorlink=Georg Bauer |author=Bauer Georg, Bandy Mark Chance (tr.), Bandy Jean A.(tr.) |title=De Natura Fossilium |originallanguage={{la icon}} |work=vi |year=1546}} translated 1955
*{{Cite book| last = Hyne| first = Norman J.| title = Nontechnical Guide to Petroleum Geology, Exploration, Drilling, and Production| year = 2001| publisher = PennWell Corporation| isbn = 087814823X}}
*{{cite book|last=Mabro|first=Robert|coauthors=Organization of Petroleum Exporting Countries|title=Oil in the 21st century: issues, challenges and opportunities|publisher=Oxford Press|year=2006|isbn=0199207380, 9780199207381}}
*{{cite book|title=The Age of Oil: What They Don't Want You to Know About the World's Most Controversial Resource|page=15|author=Maugeri, Leonardo|year=2005|publisher=Globe Pequot|location=Guilford, CT|isbn=978-1-59921-118-3|url=http://books.google.com/?id=mzHt5hYeXlIC}}
*{{Cite book| last = Speight| first = James G.| title = The Chemistry and Technology of Petroleum| year = 1999| publisher = Marcel Dekker| isbn = 0824702174}}

==External links==
{{Commons|Petroleum}}
{{Wikinewspar|Economy_and_business#Commodities|Commodities}}
*{{dmoz|Science/Earth_Sciences/Geology/Petroleum|Petroleum}}
*[http://www.petroleumonline.com/ Petroleum Online e-Learning resource from IHRDC]
*[http://www.eia.doe.gov/oil_gas/petroleum/info_glance/petroleum.html U.S. Energy Information Administration]
**[http://www.eia.doe.gov/emeu/international/contents.html U.S. Department of Energy EIA – World supply and consumption]
**[http://tonto.eia.doe.gov/energy_in_brief/world_oil_market.cfm Who are the major players supplying the world oil market?]
*[http://www.api.org/ American Petroleum Institute] – the trade association of the US oil industry.
*[http://www.iea.org/Textbase/stats/surveys/oilsurv.pdf Oil survey – [[OECD]] [[International Energy Agency]] ]
*[http://www.etoolsage.com/converter/Fuelconverter.asp Oil volume-weight and price converter]
*[http://www.petrostrategies.org/Learning_Center/learning_center.htm Oil and Gas Industry Learning Center – information on oil and gas processes]
*[http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+Crude+oil U.S. National Library of Medicine: Hazardous Substances Databank – Crude Oil]
{{Petroleum industry}}

[[Category:Oils]]
[[Category:Petroleum| ]]
[[Category:Chemical mixtures]]
[[Category:Fuels]]
[[Category:Glassforming liquids and melts]]

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