The BASICS: What is petroleum, really?

What is petroleum?

Petroleum is the latin word for rock oil, “petro” meaning rock and “oleum” meaning oil. It occurs naturally in rock formations within the earth and may be found oozing out of rocks, hence the name “rock oil.” It is a thick, complex mixture of gaseous, liquid, and solid hydrocarbons
a chemical compound that contains carbon and hydrogen
and other organic molecules
carbon-containing compounds
that may contain sulfur, nitrogen, oxygen, and metals. Although the term petroleum includes only liquid crude oil in the strictest sense, in common useage, it refers to a mixture of crude oil and natural gas. Another form of petroleum is bitumen, a think, sticky, semi-solid.

You may have heard petroleum called a fossil fuel. Fossil fuels are formed by the decomposition of dead animals, plants, and microorganism that lived millions of years ago and are found in deposits beneath the earth’s surface. Learn more about fossil fuels and how they are created.

quizWhat are the most common elements found in petroleum? What elements are found in trace amounts? Rollover the periodic table to find them.

Types of petroleum

Crude Oil, the Liquid Form

newspaper story

What is crude oil?

Crude oil, which is the liquid form of petroleum, varies in appearance according to its chemical composition. It is usually found as a viscous liquid, ranging from dark to yellowish green in color. News reports often mention light and heavy crude and sweet and sour crude.

What is the difference between heavy and light crude?

Heavy and light oils differ in their densityDensity is Mass/Volume.. Light oils have densities less than 1.0 g/cc and float easily on water. By contrast, some heavy oils may be so dense that they sink, rather than float, in water. How does the presence of different density oils affect oil spill clean-up? The environment?

Although the types and proportions of hydrocarbons found in oil vary widely, the percentage of chemical elements is quite similar in all oil. The composition of petroleum by weight is mostly carbon and hydrogen, with less nitrogen, oxygen, and sulfur. Traces of iron, nickel, copper, and vanadium each make up less than 2% of the weight of oil.

Did you know crude oil can be sweet or sour?

Economic Impact

When the price of oil per barrel is quoted, it refers to light, sweet oilsSweet oils have a mildly sweet taste and somewhat pleasant smell. that are less expensive to refine into products like gasoline, kerosene, and diesel. Government regulationsThe government regulates through the U.S. EPA Tier 2 Vehicle and Gasoline Sulfur Program. require gasoline and diesel that are low in sulfur to maintain clean air standards. Because these higher quality crudes are in such high demand, the supply has diminished and prices have increased. The heavier, sour crudes are harder and more expensive to refine into usable products.

There are many reasons that the price of oil has increased. Study this graph from the Energy Information Administration to determine one reason. API gravity is a measure of how heavy or light petroleum is compared to water. As the oil becomes heavier, the API gravity decreases.

quizAccording to the graph, how has the quality of crude changed from 2000 to 2005? How would this change affect the price of petroleum products?

chart showing natural gas use in 2008

Source: Energy Information Administration, Natural Gas Annual 2008.

Natural Gas

Natural gas is a colorless, odorless, tasteless, combustible mixture of gaseous hydrocarbons. It is a clean-burning energy source that fuels the world’s economy. In the United States alone, over 60 million homes and well over 50% of retail businesses, hospitals, and offices use natural gas as an energy source. According to the Energy Information Administration, 24% of the energy used in our country in 2008 came from natural gas (see graph). Most of the gas consumed by the U.S. is produced within its own borders, but some is imported from other countries, increasingly as liquified natural gas (LNG).

Natural gas is found in deposits under the earth’s surface. Called "associated gas" if found with crude oil deposits, natural gas may be dissolved within the oil or may rise to form a separate layer above the oil because of its low density. Non-associated gas is found with little or no crude oil.

This map shows natural gas production (in cubic meters) in 2006. (Grey means no data)

map of countries with natural gas

Source: CIA Factbook Figures, 2006.

quizAccording to the map, what countries produce the most natural gas?


The composition of natural gas varies widely, containing mostly methane, and lesser amounts of
ethaneEthane is used to make ethylene, the most produced organic compound in the world. Ethylene is used to make a wide variety of products, such as plastic bags, wire and cable insulation, detergents, and chemical weapons., propanePropane is commonly used to fuel engines, portable stoves, barbeques, and to heat homes., butaneButane is used as a fuel for cooking and cigarette lighters and as a propellant in aerosol sprays., and carbon dioxide. It may also contain small amounts of oxygen, nitrogen and hydrogen sulfide gases. Extensive processing must occur before gas can be used as a fuel source. In this purifying process, almost all chemicals, other than methane, are removed from the raw gas.

The petrochemical industry uses natural gas as an essential feedstock for many of the products we use daily, including clothing, carpets, sports equipment, pharmaceuticals and medical equipment, computers, and auto parts. It is also a primary feedstock for chemicals, plastics, and fertilizers.

Bitumen, the Semi-Solid Form

Some oil is found in semi-solid form mixed with sand and water and is referred to as crude bitumen or asphalt.

liquid bitumen

Sticky bitumen. Source: De Boer Waterproofing Solutions

Bitumen is a thick, sticky, tar-like form of oil that is similar to molasses at room temperature and must be heated or diluted to flow. Most bitumens contain sulfur and heavy metals such as nickel, vanadium, lead, chromium, mercury, and also arsenic, selenium, and other toxic elements.

Bitumen is primarily used to pave roads and to waterproof objects in today’s society, but in the past, bitumen had a wide variety of uses. According to Herodotus (Herodotus, Book I, 179), bitumen was used as mortar in the walls of Bablylon. It was also used in early photographic techniques, to waterproof boats, and to provide sound insulation on equipment.

Canada and Venezuela have the largest deposits of bitumen. In fact, Canada’s huge bitumen deposits cover an area the size of England, giving it the second largest known oil reserves in the world. Every year workers dig up about $50 million worth of asphalt or bitumen.

quizCan you find Canada and Venezuela on this map?

quizStudy the table to answer these questions:
What type of petroleum contains the most oxygen? Nitrogen? Sulfur?
Are the carbon and the hydrogen contents similar in all samples?

Element Crude oil Bitumen Natural gas
Carbon 65-80% 85% 80.2%
Hydrogen 20-25% 12% 7.5%
Oxygen trace >2% 7.6%
Nitrogen 1-15% >1.5% 1.7%
Sulphur >0.2% >3% 3%

Source: OpenLearn Learning Space, Module on Petroleum

From Petroleum to Petrochemicals

Petrochemicals are chemicals made from crude oil and natural gas.

Primary petrochemicals include olefinsOlefins are any unsaturated hydrocarbons, containing at least one carbon-carbon double bond, aromaticsAromatic compounds contain at least one ring with six carbon atoms, each bonded to least two other carbons. Each carbon is joined to one adjacent carbon by a single bond, and to another adjacent carbon by a double bond and methanolMethanol is the simplest alcohol, with one carbon and one hydroxyl group. Ethylene and propylene are the major olefins, and because of their highly reactive double bond, may be changed into many different compounds. Aromatics, which contain at least one six-carbon ring, include compounds such as benzene, toluene, and xylenes. Methanol is the simplest alcohol. These primary petrochemicals are used to make over 4,000 products, including detergents, fertilizers, insecticides, gasoline, medicines, paints, synthetic fibers, synthetic rubber, and plastics.

quizIdentify these compounds as methanol, olefin, or aromatic. Check your answer by rolling over each structure.

pump jack

how much?

In 2006, the world consumed more than 3.5 billion gallons of oil each day [source: U.S. Department of Energy].


energy map

Source: EIA

Find out your state's energy profile.


For more stats about the U.S. oil supply, check out the Energy Information Administration. E I A logo




crude makes news

Oil & Gas News (newsfeed from Yahoo News)

Top Oil News (blog with peak oil news and prices)

Energy Industry Today (OPEC headlines by region)

Commodities Update (oil prices from CNN Money)

Recent Crude Oil Trends (from Metal Prices)

metal prices chart

the pipeline

Oil and gas are transported by several methods, including tankers, trucks, and trains. But the real mover is the pipeline.

above-ground pipeline in alaska

Source: National Renewable Energy Lab, Credit: Bruce Green

The U.S. has over 300,000 miles of pipelines running through every single state. Most of the major pipelines are made of steel and measure 24-36 inches in diameter.

smell a leak?

Q: If natural gas is odorless and colorless, how would a gas leak possibly be detected?

funny face

A: Mercaptan, a chemical that smells like sulfur and rotten eggs, is added to natural gas before distribution.

The distinctly bad smell lets you know if you have a gas leak. The discovery of leaks is extremely important because gas is highly flammable.

liquified gas?

LNG is liqufied natural gas. You may liqufy and thus reduce the volume of a gas by cooling.

LNG is natural gas that is cooled to -260°F and occupies a volume about 600 times less than the volume of its gaseous state.

gas storage tank

Source: Wikipedia

In this "compacted" form, natural gas can be shipped in tankers across oceans or transported by trucks across land to places where pipelines can't reach.

lake pitch

Lake Pitch in Trinidad is the largest source of asphalt or bitumen. Check out the goo!

lake pitch

Source: Wikipedia

Sir Walter Raleigh found the lake in 1595 and used some of the asphalt to plug cracks in his ship.

Read more about Lake Pitch in this blog.

petrochemical = what?

A ton of products that you use everyday are made from petrochemicals:

  • Panty hose
  • Bicycle helmets
  • Gasoline
  • Fishing rods
  • Sunglasses
  • Crayons
  • Shampoo
  • Masking tape
  • Pens
  • Medicines
  • Paints
  • Trash bags
  • Tires
  • Toothpaste tubes
  • Balloons
  • Artificial limbs
  • Plastics (yes, all of them)
  • Credit cards