Chemical Composition of Petroleum

Petroleum Composition

Oil pump
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Petroleum or crude oil is a complex mixture of hydrocarbons and other chemicals. The composition varies widely depending on where and how the petroleum was formed. In fact, chemical analysis can be used to fingerprint the source of petroleum. However, raw petroleum or crude oil has characteristic properties and composition.

Hydrocarbons in Crude Oil

There are four main types of hydrocarbons found in crude oil.

  1. paraffins (15-60%)
  2. naphthenes (30-60%)
  3. aromatics (3-30%)
  4. asphaltics (remainder)

The hydrocarbons primarily are alkanes, cycloalkanes, and aromatic hydrocarbons.

Elemental Composition of Petroleum

Although there is considerable variation between the ratios of organic molecules, the elemental composition of petroleum is well-defined:

  1. Carbon - 83 to 87%
  2. Hydrogen - 10 to 14%
  3. Nitrogen - 0.1 to 2%
  4. Oxygen - 0.05 to 1.5%
  5. Sulfur - 0.05 to 6.0%
  6. Metals - < 0.1%

The most common metals are iron, nickel, copper, and vanadium.

Petroleum Color and Viscosity

The color and viscosity of petroleum vary markedly from one place to another. Most petroleum is dark brown or blackish in color, but it also occurs in green, red, or yellow.


  • Norman, J. Hyne (2001). Nontechnical guide to petroleum geology, exploration, drilling, and production (2nd ed.). Tulsa, OK: Penn Well Corp. ISBN 978-0-87814-823-3. 
  • Ollivier, Bernard; Magot, Michel (January 1, 2005). Petroleum Microbiology. Washington, DC: American Society of Microbiology. doi:10.1128/9781555817589. ISBN 978-1-55581-758-9.
  • Speight, James G. (1999). The Chemistry and Technology of Petroleum (3rd ed.). New York: Marcel Dekker. ISBN 978-0-8247-0217-5. 
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Helmenstine, Anne Marie, Ph.D. "Chemical Composition of Petroleum." ThoughtCo, Feb. 16, 2021, Helmenstine, Anne Marie, Ph.D. (2021, February 16). Chemical Composition of Petroleum. Retrieved from Helmenstine, Anne Marie, Ph.D. "Chemical Composition of Petroleum." ThoughtCo. (accessed March 30, 2023).