Petroleum (also known as crude oil or simply oil) is a fossil fuel that was formed from the remains of ancient marine organisms.

Millions of years ago, algae and plants lived in shallow seas. After dying and sinking to the seafloor, the organic material mixed with other sediments and was buried. Over millions of years under high pressure and high temperature, the remains of these organisms transformed into what we know today as fossil fuels. Coal, natural gas and petroleum are all fossil fuels that formed under similar conditions.

Today, petroleum is found in vast underground reservoirs where ancient seas were located. Petroleum reservoirs can be found beneath land or the ocean floor. Their crude oil is extracted with giant drilling machines.

Crude oil is usually black or dark brown, but can also be yellowish, reddish, tan or even greenish. Variations in color indicate the distinct chemical compositions of different supplies of crude oil.

Petroleum is used to make gasoline, an important product in our everyday lives. It is also processed and part of thousands of different items, including tires, refrigerators, life jackets and anesthetics.

When petroleum products such as gasoline are burned for energy, they release toxic gases and high amounts of carbon dioxide, a greenhouse gas. Carbon helps regulate the Earth's atmospheric temperature, and adding to the natural balance by burning fossil fuels adversely affects our climate.

There are huge quantities of petroleum found under Earth's surface and in tar pits that bubble to the surface. However, petroleum, like coal and natural gas, is a non-renewable source of energy. It took millions of years for it to form, and when it is extracted and consumed, there is no way for us to replace it.

Oil supplies will run out. Eventually, the world will reach "peak oil," or its highest production level. Some experts predict peak oil could come as soon as 2050. Finding alternatives to petroleum is crucial to global energy use, and is the focus of many industries.

Formation of Petroleum

The geological conditions that would eventually create petroleum formed millions of years ago, when plants, algae and plankton drifted in oceans and shallow seas. These organisms sank to the seafloor at the end of their life cycle. Over time, they were buried and crushed under millions of tons of sediment and even more layers of plant debris.

Eventually, ancient seas dried up and dry basins remained, called sedimentary basins. Deep under the basin floor, the organic material was compressed between Earth's mantle, with very high temperatures, and millions of tons of rock and sediment above. Oxygen was almost completely absent in these conditions, and the organic matter began to transform into a waxy substance called kerogen.

With more heat, time and pressure, the kerogen underwent a process called catagenesis, and transformed into hydrocarbons. Hydrocarbons are simply chemicals made up of hydrogen and carbon. Different combinations of heat and pressure can create different forms of hydrocarbons. Some other examples are coal, peat and natural gas.

Sedimentary basins, where ancient seabeds used to lie, are sometimes sources of petroleum. In Africa, the Niger Delta sedimentary basin covers land in Nigeria, Cameroon and Equatorial Guinea. More than 500 oil deposits have been discovered in the massive Niger Delta basin, and they comprise one of the most productive oil fields in Africa.

Chemistry and Classification of Crude Oil

The gasoline we use to fuel our cars, the synthetic fabrics of our backpacks and shoes, and the thousands of different useful products made from petroleum come in forms that are consistent and reliable. However, the crude oil from which these items are produced is neither consistent nor uniform.

Chemistry

Crude oil is composed of hydrocarbons, which are mainly hydrogen (about 13 percent by weight) and carbon (about 85 percent). Other elements such as nitrogen (about 0.5 percent), sulfur (0.5 percent), oxygen (one percent), and metals such as iron, nickel and copper (less than 0.1 percent) can also be mixed in with the hydrocarbons in small amounts. The way molecules are organized in the hydrocarbon is a result of the original composition of the algae, plants or plankton from millions of years ago. The amount of heat and pressure the plants were exposed to also contributes to variations that are found in hydrocarbons and crude oil.

Due to this variation, crude oil that is pumped from the ground can consist of hundreds of different petroleum compounds. Light oils can contain up to 97 percent hydrocarbons, while heavier oils and bitumens might contain only 50 percent hydrocarbons and larger quantities of other elements. It is almost always necessary to refine crude oil in order to make useful products.

Classification

Oil is classified according to three main categories: the geographic location where it was drilled, its sulfur content and its API gravity (a measure of density).

Classification: Geography

Oil is drilled all over the world. However, there are three primary sources of crude oil that set reference points for ranking and pricing other oil supplies: Brent Crude, West Texas Intermediate and Dubai and Oman.

Brent Crude is a mixture that comes from 15 different oil fields between Scotland and Norway in the North Sea. These fields supply oil to most of Europe.

West Texas Intermediate (WTI) is a lighter oil that is produced mostly in the U.S. state of Texas. It is "sweet" and "light"—considered very high quality. WTI supplies much of North America with oil.

Dubai crude, also known as Fateh or Dubai-Oman crude, is a light, sour oil that is produced in Dubai, part of the United Arab Emirates. The nearby country of Oman has recently begun producing oil. Dubai and Oman crudes are used as a reference point for pricing Persian Gulf oils that are mostly exported to Asia.

The OPEC Reference Basket is another important oil source. OPEC is the Organization of the Petroleum Exporting Countries founded in 1960 by Iran, Iraq, Kuwait, Saudi Arabia and Venezuela. Other countries have joined or left the organization from that time. The OPEC Reference Basket is the average price of petroleum from OPEC's member countries.

Classification: Sulfur Content

Sulfur is considered an "impurity" in petroleum. Sulfur in crude oil can corrode metal in the refining process and contribute to air pollution. Petroleum with more than 0.5 percent sulfur is called "sour," while petroleum with less than 0.5 percent sulfur is "sweet."

Sweet oil is usually much more valuable than sour because it does not require as much refining and is less harmful to the environment.

Classification: API Gravity

The American Petroleum Institute (API) is a trade association for businesses in the oil and natural gas industries. The API has established accepted systems of standards for a variety of oil- and gas-related products, such as gauges, pumps and drilling machinery. The API has also established several units of measurement. The "API unit," for instance, measures gamma radiation in a borehole (a shaft drilled into the ground).

API gravity is a measure of the density of petroleum liquid compared to water. If a petroleum liquid's API gravity is greater than 10, it is "light," and floats on top of water. If the API gravity is less than 10, it is "heavy," and sinks in water.

Light oils are preferred because they have a higher yield of hydrocarbons. Heavier oils have greater concentrations of metals and sulfur and require more refining.

Petroleum Reservoirs

Petroleum is found in underground pockets called reservoirs. Deep beneath the Earth, pressure is extremely high. Petroleum slowly seeps out toward the surface, where there is lower pressure. It continues this movement from high to low pressure until it encounters a layer of rock that is impermeable. The petroleum then collects in reservoirs, which can be several hundred meters below the surface of Earth.

Petroleum can be contained by structural traps, which are formed when massive layers of rock are bent or faulted (broken) from Earth's shifting land masses. Oil can also be contained by stratigraphic traps. Different strata, or layers of rock, can have different amounts of porosity. Crude oil migrates easily through a layer of sandstone, for instance, but would be trapped beneath a layer of shale.

Geologists, chemists and engineers look for geological structures that typically trap petroleum. They use a process called "seismic reflection" to locate underground rock structures that might have trapped crude oil. During the process, a small explosion is set off. Sound waves travel underground, bounce off of the different types of rock, and return to the surface. Sensors on the ground interpret the returning sound waves to determine the underground geological layout and possibility of a petroleum reservoir.

The amount of petroleum in a reservoir is measured in barrels or tons. An oil barrel is about 42 gallons. This measurement is usually used by oil producers in the United States. Oil producers in Europe and Asia tend to measure in metric tons. There are about six to eight barrels of oil in a metric ton.

Crude oil is frequently found in reservoirs along with natural gas. Sometimes, natural gas is either burned or allowed to escape into the atmosphere. Technology has also been developed to capture the natural gas and either re-inject it into the well or compress it into liquid natural gas (LNG). LNG is easily transportable and has versatile uses.

Extracting Petroleum

The total amount of petroleum in a reservoir is called oil-in-place. Many petroleum liquids that make up a reservoir's oil-in-place are unable to be extracted. These petroleum liquids may be too difficult, dangerous or expensive to drill. The part of a reservoir's oil-in-place that can be extracted and refined is that reservoir's oil reserves.

Drilling can either be developmental, exploratory or directional.

Drilling in an area where oil reserves have already been found is called developmental drilling. Prudhoe Bay, Alaska, United States, has the largest oil reserves in the United States. Developmental drilling in Prudhoe Bay includes new wells and expanding extraction technology.

Drilling where there are no known reserves is called exploratory drilling. Exploratory, also called "wildcat" drilling, is a risky business with a very high failure rate. However, the potential rewards of striking oil tempt many "wildcatters" to attempt exploratory drilling. "Diamond" Glenn McCarthy, for example, is known as the "King of the Wildcatters" because of his success in discovering the massive oil reserves near Houston, Texas, United States. McCarthy struck oil many times in the 1930s, earning millions of dollars.

Directional drilling involves drilling vertically to a known source of oil, then veering the drill bit at an angle to access additional resources. Accusations of directional drilling led to the first Gulf War in 1991. Iraq accused Kuwait of using directional drilling techniques to extract oil from Iraqi oil reservoirs near the Kuwaiti border. Iraq subsequently invaded Kuwait, an act which drew international attention and intervention. After the war, the border between Iraq and Kuwait was redrawn, with the reservoirs now belonging to Kuwait.

Oil Rigs

On land, oil can be drilled with an apparatus called an oil rig or drilling rig. Offshore, oil is drilled from an oil platform.

Primary Production

Most modern wells use an air rotary drilling rig, which can operate 24 hours a day. In this process, engines power a drill bit. A drill bit is a cutting tool used to create a circular hole. The drill bits used in air rotary drilling rigs are hollow steel, with tungsten rods used to cut the rock.

As the drill bit rotates and cuts through the earth, small pieces of rock are chipped off. A powerful flow of air is pumped down the center of the hollow drill, and comes out through the bottom of the drill bit. The air then rushes back toward the surface, carrying with it tiny chunks of rock. Geologists on site can study these pieces of pulverized rock to determine the different rock strata the drill encounters.

When the drill hits oil, some of the oil naturally rises from the ground, moving from an area of high pressure to low pressure. This immediate release of oil can be a "gusher," shooting dozens of meters into the air, one of the most dramatic extraction activities. It is also one of the most dangerous, and a piece of equipment called a blowout preventer redistributes pressure to stop such a gusher.

Pumps are used to extract oil. "Mud" is the drilling fluid used to create boreholes for extracting oil and natural gas. Mud pumps circulate drilling fluid.

The petroleum industry uses a wide variety of extraction pumps. Which pump to use depends on the geography, quality and position of the oil reservoir. Submersible pumps, for example, are submerged directly into the fluid. A gas lift uses compressed air to force the petroleum to the surface or well.

One of the most familiar types of extraction pumps is the pumpjack, the upper part of a piston pump. Pumpjacks are nicknamed "thirsty birds" or "nodding donkeys" for their controlled, regular dipping motion. A crank moves the large, hammer-shaped pumpjack up and down. Far below the surface, the motion of the pumpjack moves a hollow piston up and down, constantly carrying petroleum back to the surface or well.

Secondary Recovery

Even after pumping, the majority of the oil can remain tightly trapped in the underground reservoir. Other methods are necessary to extract this petroleum, a process called secondary recovery.

Water flooding was discovered by accident. In the 1870s, oil producers in Pennsylvania noticed that abandoned oil wells were accumulating rainwater and groundwater. The weight of the water in the boreholes forced oil out of the reservoirs and into nearby wells, increasing their production. Oil producers soon began intentionally flooding wells as a way to extract more oil.

Oil Platforms

Drilling offshore is much more expensive than drilling onshore. It usually uses the same drilling techniques as onshore, but requires a massive structure that can sustain the tremendous strength of ocean waves in stormy seas.

Offshore drilling platforms are some of the largest manmade structures in the world. They often include housing accommodations for people who work on the platform, as well as docking facilities and a helicopter landing pad to transport workers.

The platform can either be tethered to the ocean floor and float, or can be a rigid structure that is fixed to the bottom of the ocean, sea or lake with concrete or steel legs.

The Hibernia platform, 315 kilometers (196 miles) off Canada's eastern shore in the North Atlantic Ocean, is one of the world's largest oil platforms. More than 70 people work on the platform in three-week shifts. The platform is about 225 meters (738 feet) tall and is anchored to the ocean floor. About 450,000 tons of solid ballast were added to give it additional stability. The platform can store up to 1.3 million barrels of oil. In total, Hibernia weighs 1.2 million tons! However, the platform is still vulnerable to the crushing weight and strength of icebergs. Its edges are serrated and sharp to withstand the impact of sea ice or icebergs.

Oil platforms can cause enormous environmental disasters. Problems with the drilling equipment can cause the oil to explode out of the well and into the ocean. Repairing the well hundreds of meters below the ocean is extremely difficult, expensive and slow. Millions of barrels of oil can spill into the ocean before the well is plugged.

A massive oil platform in the Gulf of Mexico, the Deepwater Horizon, exploded in 2010. This was the largest accidental marine oil spill in history. Eleven platform workers died, and more than four million barrels of oil gushed into the Gulf of Mexico. More than 40,000 barrels flowed into the ocean every day. Eight national parks were threatened, the economies of communities along the Gulf Coast were threatened as the tourism and fishing industries declined and more than 6,000 animals died.

Rigs to Reefs

Offshore oil platforms can also act as artificial reefs. They provide a surface (substrate) for algae, coral, oysters and barnacles. This artificial reef can attract fish and marine mammals, and create a thriving ecosystem.

Until the 1980s, oil platforms were deconstructed and removed from the oceans, and the metal was sold as scrap. In 1986, the National Marine Fisheries Association developed the Rigs-to-Reefs Program. Now, oil platforms are either toppled (by underwater explosion), removed and towed to a new location, or partially deconstructed. This allows the marine life to continue flourishing on the artificial reef that had provided habitats for decades.

The environmental impact of the Rigs-to-Reefs Program is still being studied. Fishing boats have had their nets caught in the platforms, and there are concerns about safety regulations of the abandoned structures.

Petroleum and the Environment: Bitumen and the Boreal Forest

Crude oil does not always have to be extracted through deep drilling. If it does not encounter rocky obstacles underground, it can seep all the way to the surface and bubble above ground. Bitumen is a form of petroleum that is black, extremely sticky and sometimes rises to Earth's surface.

In its natural state, bitumen is typically mixed with "oil sands" or "tar sands," which makes it extremely difficult to extract and an unconventional source of oil. Only about 20 percent of the world's reserves of bitumen are above ground and can be surface-mined.

Unfortunately, because bitumen contains high amounts of sulfur and heavy metals, extracting and refining it is both costly and harmful to the environment. Producing bitumen into useful products releases 12-24 percent more carbon emissions than processing conventional oil.

Bitumen is about the consistency of cold molasses, and powerful hot steam has to be pumped into the well in order to melt the bitumen to extract it. Large quantities of water are then used to separate the bitumen from sand and clay. This process depletes nearby water supplies. Releasing the treated water back into the environment can further contaminate the remaining water supply.

Processing bitumen from tar sands is also a complex, expensive procedure. It takes two tons of oil sands to produce one barrel of oil.

However, we depend on bitumen for its unique properties: about 85 percent of the bitumen extracted is used to make asphalt to pave and patch our roads. A small percentage is used for roofing and other products.

Bitumen Reserves

Most of the world's tar sands are in the eastern part of Alberta, Canada, in the Athabasca Oil Sands. Other major reserves are in the North Caspian Basin of Kazahkstan and Siberia, Russia.

Unfortunately, the bitumen reserves are located beneath part of the boreal forest, also called the taiga. This makes extraction both difficult and environmentally dangerous.

The taiga circles the Northern Hemisphere just below the frozen tundra, mostly in Canada, Russia and Scandinavia. It accounts for almost one-third of all of the forested land on the planet.

The taiga is sometimes called the "lungs of the planet" because it filters tons of water and oxygen through the leaves and needles of its trees every day. Every spring, the boreal forest releases immense amounts of oxygen into the atmosphere and keeps our air clean. It is home to a mosaic of plant and animal life, all of which depend on the mature trees, mosses and lichen of the boreal biome.

Surface mines are estimated to only take up 0.2 percent of Canada's boreal forest. About 80 percent of Canada's oil sands can be accessed through drilling, and 20 percent by surface mining.

Refining Petroleum

Refining petroleum is the process of converting crude oil or bitumen into more useful products, such as fuel or asphalt.

Crude oil comes out of the ground with impurities, from sulfur to sand. These components have to be separated. This is done by heating the crude oil in a distillation tower that has trays and temperatures set at different levels. Oil's hydrocarbons and metals have different boiling temperatures, and when the oil is heated, vapors from the different elements rise to different levels of the tower before condensing back into a liquid on the tiered trays.

Propane, kerosene and other components condense on different tiers of the tower and can be individually collected. They are transported by pipeline, ocean vessels and trucks to different locations, to either be used directly or further processed.

Petroleum Industry

Oil was not always extracted, refined and used by millions of people as it is today. However, it has always been an important part of many cultures.

The earliest known oil wells were drilled in China. The wells were drilled almost 244 meters (800 feet) deep using strong bamboo bits. The oil was extracted and transported through bamboo pipelines. It was burned as a heating fuel and industrial component. Chinese engineers burned petroleum to evaporate brine and produce salt.

On the west coast of North America, Indigenous people used bitumen as an adhesive to make canoes and baskets water-tight, and as a binder for creating ceremonial decorations and tools.

By the 7th century, Japanese engineers discovered that petroleum could be burned for light. Oil was later distilled into kerosene by a Persian alchemist in the 9th century. During the 1800s, petroleum slowly replaced whale oil in kerosene lamps, producing a radical decline in whale hunting.

The modern oil industry was established in the 1850s. The first well was drilled in Poland in 1853, and the technology spread to other countries and was improved.

The Industrial Revolution created a vast new opportunity for the use of petroleum. Machinery powered by steam engines quickly became too slow, small-scale and expensive. Petroleum-based fuel was in demand. The invention of the mass-produced automobile in the early 20th century further increased demand for petroleum.

Petroleum production has rapidly increased. In 1859, the U.S. produced 2,000 barrels of oil. By 1906, that number was 126 million barrels per year. Today, the U.S. produces about 6.8 billion barrels of oil every year.

According to OPEC, more than 70 million barrels are produced worldwide every day. That is almost 49,000 barrels per minute.

Although that seems like an impossibly high amount, the uses for petroleum have expanded to almost every area of life. Petroleum makes our lives easy in many ways. In many countries, including the U.S., the oil industry provides millions of jobs, from surveyors and platform workers to geologists and engineers.

The United States consumes more oil than any other country. In 2017, the U.S. consumed more than 19 million barrels of oil every day. This is more than all of the oil consumed in Latin America (9.5 million) and Eastern Europe and Eurasia (5.5 million) combined.

Petroleum is an ingredient in thousands of everyday items. The gasoline that we depend on for transportation to school, work or vacation comes from crude oil. A barrel of petroleum produces about 72 liters (19 gallons) of gasoline, and is used by people all over the world to power cars, boats, jets and scooters.

Diesel-powered generators are used in many remote homes, schools and hospitals. During emergencies, when the power grid is interrupted, diesel generators save lives by providing electricity to hospitals, apartment complexes, schools and other buildings that would otherwise be cold and "in the dark."

Petroleum is also used in liquid products such as nail polish, rubbing alcohol and ammonia. Petroleum is found in recreational items as diverse as surfboards, footballs and basketballs, bicycle tires, golf bags, tents, cameras and fishing lures.

Petroleum is also contained in more essential items such as artificial limbs, water pipes and vitamin capsules. In our homes, we are surrounded by and depend on products that contain petroleum. House paint, trash bags, roofing, shoes, telephones, hair curlers and even crayons contain refined petroleum.

Carbon Cycle

There are major disadvantages to extracting fossil fuels, and extracting petroleum is a controversial industry.

Carbon, an essential element on Earth, makes up about 85 of the hydrocarbons in petroleum. Carbon constantly cycles between the water, land and atmosphere.

Carbon is absorbed by plants and is part of every living organism as it moves through the food web. Carbon is naturally released through volcanoes, soil erosion and evaporation. When carbon is released into the atmosphere, it absorbs and retains heat, regulating Earth's temperature and making our planet habitable.

Not all of the carbon on Earth is involved in the carbon cycle above ground. Vast quantities of it are sequestered, or stored, underground, in the form of fossil fuels and in the soil. This sequestered carbon is necessary because it keeps the Earth's "carbon budget" balanced.

However, that budget is falling out of balance. Since the Industrial Revolution, fossil fuels have been aggressively extracted and burned for energy or fuel. This releases the carbon that has been sequestered underground and upsets the carbon budget. This affects the quality of our air, water and overall climate.

The taiga, for example, sequesters vast amounts of carbon in its trees and below the forest floor. Drilling for natural resources not only releases the carbon stored in the fossil fuels, but also the carbon stored in the forest itself.

Combusting gasoline, which is made from petroleum, is particularly harmful to the environment. Every 3.8 liters (one gallon) of ethanol-free gas that is combusted in a car's engine releases about 9 kilograms (20 pounds) of carbon dioxide into the environment. (Gasoline infused with 10 percent ethanol releases about eight kilograms (17 pounds.)) Diesel fuel releases about 10 kilograms (22 pounds) of carbon dioxide, while biodiesel (diesel with 10 percent biofuel) emits about nine kilograms (20 pounds).

Gasoline and diesel also directly pollute the atmosphere. They emit toxic compounds and particulates, including formaldehyde and benzene.

People and Petroleum

Oil is a major component of modern civilization. In developing countries, access to affordable energy can empower citizens and lead to higher quality of life. Petroleum provides transportation fuel, is a part of many chemicals and medicines, and is used to make crucial items such as heart valves, contact lenses and bandages. Oil reserves attract outside investment and are important for improving countries' overall economy.

However, in some countries, having access to oil can lead government to be less democratic a situation nicknamed a "petro-dictatorship." Russia, Nigeria and Iran have all been accused of having petro-authoritarian regimes.

Peak Oil

Oil is a nonrenewable resource, and the world's oil reserves will not always be enough to provide for the world's demand for petroleum. Peak oil is the point when the oil industry is extracting the maximum possible amount of petroleum. After peak oil, petroleum production will only decrease. After peak oil, there will be a decline in production and a rise in costs for the remaining supply.

Measuring peak oil uses the reserves-to-production ratio (RPR). This ratio compares the amount of proven oil reserves to the current extraction rate. The reserves-to-production ratio is expressed in years.

According to one industry report, the United States has an RPR of about nine years. The oil-rich, developing nation of Iran, which has a much lower consumption rate, has an RPR of more than 80 years.

It is impossible to know the precise year for peak oil. Some geologists argue it has already passed, while others maintain that extraction technology will delay peak oil for decades. Many geologists estimate that peak oil might be reached within 20 years.

Petroleum Alternatives

Individuals, industries and organizations are increasingly concerned with peak oil and environmental consequences of petroleum extraction. Alternatives to oil are being developed in some areas and governments and organizations are encouraging citizens to change their habits so we do not rely so heavily on oil. Bioasphalts, for example, are asphalts made from renewable sources such as molasses, sugar, corn, potato starch, or even byproducts of oil processes.

Algae is also a potentially enormous source of energy. Algae oil (so-called "green crude") can be converted into a biofuel. Algae grows extremely quickly and takes up a fraction of the space used by other biofuel feedstocks. About 38,849 square kilometers (15,000 square miles) of algae—less than half the size of the U.S. state of Maine—would provide enough biofuel to replace all of the U.S.'s petroleum needs. Algae absorbs pollution, releases oxygen, and does not require freshwater.

The country of Sweden has made it a priority to drastically reduce its dependence on oil and other fossil fuel energy by 2020. Experts in agriculture, science, industry, forestry and energy have come together to develop sources of sustainable energy, including geothermal heat pumps, wind farms, wave and solar energy and domestic biofuel for hybrid vehicles. Changes in society's habits, such as increasing public transportation and video-conferencing for businesses, are also part of the plan to decrease oil use.