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 fuel
s. Components of petroleum are separated using a technique called fractional distillation
, 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
s of various molecular weights and may contain miscellaneous organic compound
s. The name ''petroleum'' covers both naturally occurring unprocessed crude oil and petroleum product
s that are made up of refined crude oil. A fossil fuel
, petroleum is formed when large quantities of dead organisms, mostly zooplankton
, are buried underneath sedimentary rock
and subjected to both intense heat and pressure.
Petroleum has mostly been recovered by oil drilling
. 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
and oil shale
. Once extracted, oil is refined and separated, most easily by distillation
, into numerous products for direct use or use in manufacturing, such as gasoline
and chemical reagent
s used to make plastic
s and pharmaceuticals
. Petroleum is used in manufacturing a wide variety of materials,
and it is estimated that the world consumes about 100 million barrels
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
", 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
of petroleum fuels all release large quantities of greenhouse gas
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
. Other negative environmental effects
include the environmental impacts of exploration and exploitation of petroleum reserves, such as oil spill
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 state-led-wars
and other kinds of conflicts (for example, oil revenue funded
the Islamic State of Iraq and the Levant
). Production of petroleum is expected to reach peak oil
before 2040 as global economies reduce dependencies on petroleum as part of climate change mitigation
and a transition towards renewable energy
. This is expected to have significant economic impacts that stakeholders argue need to be anticipated by a just transition
and addressing the stranded asset
s of the petroleum industry.
The word ''petroleum'' comes from Medieval Latin
(literally "rock oil"), which comes from Latin
'', "rock", (from grc|πέτρα|translit=petra, "rock") and Latin ''oleum
'', "oil", (from grc|ἔλαιον|translit=élaion, "oil").
The term was used in the treatise ''De Natura Fossilium
'', 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
s produced by distillation from mined organic solids such as cannel coal
(and later oil shale
) 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.
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
, the rise in commercial aviation
, 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
and Diodorus Siculus
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
Great quantities of it were found on the banks of the river Issus
, one of the tributaries of the Euphrates
. Ancient Persian 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
, 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.
was often distilled by Persian chemists
, with clear descriptions given in Arabic handbooks such as those of Muhammad ibn Zakarīya Rāzi
(Rhazes). The streets of Baghdad
were paved with tar
, derived from petroleum that became accessible from natural fields in the region. In the 9th century, oil field
s were exploited in the area around modern Baku
. These fields were described by the Arab geographer Abu al-Hasan 'Alī al-Mas'ūdī
in the 10th century, and by Marco Polo
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
products for military purposes. Through Islamic Spain
, distillation became available in Western Europe
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
and other Iroqouis
in Western Pennsylvania
as early as 1415-1450. The French General Louis-Joseph de Montcalm
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
documented a flourishing oil extraction industry based in Yenangyaung
that, in 1795, had hundreds of hand-dug wells under production.
(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 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.
Chemist James Young
noticed a natural petroleum seepage in the Riddings colliery
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
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
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
in West Lothian
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
. 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
'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
1858 in Wietze
, 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
in 1853, and another in nearby Romania
in 1857. At around the same time the world's first, small, oil refinery was opened at Jasło
in Poland, with a larger one opened at Ploiești
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
(then Canada West
[Oil Museum of Canada, Black Gold: Canada's Oil Heritage, Oil Springs: Boom & Bust](_blank)
Businessman James Miller Williams
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
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
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
company in Azerbaijan
, 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
, during which oil facilities were a major strategic asset and were extensively bombed
. The German invasion of the Soviet Union
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
imposed an oil embargo
against the United States, United Kingdom, Japan and other Western nations which supported Israel
in the Yom Kippur War
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
The top three oil producing countries are Russia
, Saudi Arabia
and the United States
. In 2018, due in part to developments in hydraulic fracturing
and horizontal drilling
, 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
, United Arab Emirates
. A large portion of the world's total oil exists as unconventional sources, such as bitumen
in Athabasca oil sands
and extra heavy oil
in the Orinoco Belt
. 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.
Petroleum includes not only crude oil, but all liquid, gaseous and solid hydrocarbon
s. Under surface pressure and temperature conditions
, lighter hydrocarbons methane
exist as gases, while pentane
and heavier hydrocarbons are in the form of liquids or solids. However, in an underground oil reservoir
the proportions of gas, liquid, and solid depend on subsurface conditions and on the phase diagram
of the petroleum mixture.
An oil well
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
and be recovered (or burned) as ''associated gas'' or ''solution gas''. A gas well
produces predominantly natural gas
. However, because the underground temperature is higher than at the surface, the gas may contain heavier hydrocarbons such as pentane, hexane
, and heptane
in the gaseous state
. At surface conditions these will condense
out of the gas to form "natural gas condensate
", often shortened to ''condensate.'' Condensate resembles gasoline in appearance and is similar in composition to some volatile light crude oil
The proportion of light hydrocarbons in the petroleum mixture varies greatly among different oil fields
, 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
The hydrocarbons in crude oil are mostly alkane
s and various aromatic hydrocarbon
s, while the other organic compounds contain nitrogen
, and trace amounts of metals such as iron, nickel, copper and vanadium
. 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
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
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
in Canada, where it is usually referred to as crude bitumen
. 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
, 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 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
and gasoline, both important ''"primary energy
"'' 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
. 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 transportability and 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, and plastics; the 16 percent not used for energy production is converted into these other materials. Petroleum is found in porous rock formations
in the upper strata
of some areas of the Earth's crust
. There is also petroleum in oil sands (tar sands)
. Known oil reserves
are typically estimated at around 190 km3
(1.2 trillion (short scale) barrels
) 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.
Petroleum is a mixture of a very large number of different hydrocarbon
s; the most commonly found molecules are alkane
s (paraffins), 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 saturated
hydrocarbons with straight or branched chains which contain only carbon
and have the general formula Cn
. 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
) to octane
) are refined
into gasoline, the ones from nonane
) to hexadecane
) into diesel fuel
and jet fuel
. Alkanes with more than 16 carbon atoms can be refined 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 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 liquefied petroleum gas
under pressure, or used to power the refinery's own burners. During the winter, butane (C4
), 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 Cn
. 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
s, to which hydrogen atoms are attached with the formula Cn
. 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 gasoline, jet fuel, kerosene, and other hydrocarbons. For example, 2,2,4-trimethylpentane
(isooctane), widely used in gasoline
, has a chemical formula of C8
and it reacts with oxygen exothermic
+ 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
, then separated in a gas chromatograph
, and finally determined with a suitable detector
, such as a flame ionization detector
or a mass spectrometer
. 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
. Due to the high temperatures and high pressures involved, exhaust gases from gasoline combustion in car engines usually include nitrogen oxide
s which are responsible for creation of photochemical smog
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:
is measured in calories per gram and
is the specific gravity
The thermal conductivity
of petroleum based liquids can be modeled as follows: