Crude Oil

Crude oil is a liquid made up of a mixture of hydrocarbons of varying densities. It is refined by means of a distillation process in which the hydrocarbons are heated which separates out the various components, or fractions, according to their respective boiling points. Lower density fractions have lower boiling points than heavier, higher density fractions. The heavier oil products produced by a fractional distillation plant can be further refined by passing them through another plant which 'cracks', or splits, the molecules into the lighter, more valuable fractions. The lightest, lowest density crudes yield a greater proportion of higher value oil products such as gasoline and thus command a higher price on world markets.

See also: Brent, WTI, API, http://www.iea.org/, http://www.eia.doe.gov/