crude oil

Crude Oil Components

Petroleum - English
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On average, crude oil are made of the following elements or compounds:

  • Carbon – 84%
  • Hydrogen – 14%
  • Sulfur – 1 to 3% (hydrogen sulfide, sulfides, disulfides, elemental sulfur)
  • Nitrogen – less than 1% (basic compounds with amine groups)
  • Oxygen – less than 1% (found in organic compounds such as carbon dioxide, phenols, ketones, carboxylic acids)
  • Metals – less than 1% (nickel, iron, vanadium, copper, arsenic)
  • Salts – less than 1% (sodium chloride, magnesium chloride, calcium chloride)

­Crude oil is the term for “unprocessed” oil, the stuff that comes out of the ground. It is also known as petroleum. Crude oil is a fossil fuel, meaning that it was made natural­ly from decaying plants and animals living in ancient seas millions of years ago — most places you can find crude oil were once sea beds. Crude oils vary in color, from clear to tar-black, and in viscosity, from water to almost solid.

Crude oils are such a useful starting point for so many different substances because they contain hydrocarbons. Hydrocarbons are molecules that contain hydrogen and carbon and come in various lengths and structures, from straight chains to branching chains to rings.

There are two things that make hydrocarbons exciting to chemists:

  • Hydrocarbons contain a lot of energy. Many of the things derived from crude oil like gasoline, diesel fuel, paraffin wax and so on take advantage of this energy.
  • Hydrocarbons can take on many different forms. The smallest hydrocarbon is methane (CH4), which is a gas that is a lighter than air. Longer chains with 5 or more carbons are liquids. Very long chains are solids like wax or tar. By chemically cross-linking hydrocarbon chains you can get everything from synthetic rubber to nylon to the plastic in Tupperware. Hydrocarbon chains are very versatile!

The major classes of hydrocarbons in crude oils include:

  • Paraffins

general formula: CnH2n+2 (n is a whole number, usually from 1 to 20)

m    straight- or branched-chain molecules

can be gasses or liquids at room temperature depending upon the molecule

examples: methane, ethane, propane, butane, isobutane, pentane, hexane

read more about Oilfield Paraffin and Asphaltene

  • Aromatics

general formula: C6H5 – Y (Y is a longer, straight molecule that connects to the benzene ring)

ringed structures with one or more rings

rings contain six carbon atoms, with alternating double and single bonds between the carbons

typically liquids

examples: benzene, napthalene

  • Napthenes or Cycloalkanes

general formula: CnH2n (n is a whole number usually from 1 to 20)

ringed structures with one or more rings

rings contain only single bonds between the carbon atoms

typically liquids at room temperature

examples: cyclohexane, methyl cyclopentane

  • Other hydrocarbons


  • general formula: CnH2n (n is a whole number, usually from 1 to 20)
  • linear or branched chain molecules containing one carbon-carbon double-bond
  • can be liquid or gas
  • examples: ethylene, butene, isobutene

Dienes and Alkynes

  • general formula: CnH2n-2 (n is a whole number, usually from 1 to 20)
  • linear or branched chain molecules containing two carbon-carbon double-bonds
  • can be liquid or gas
  • examples: acetylene, butadienes.