Petroleum Definition: Petroleum or crude oil is any naturally-occurring flammable mixture of hydrocarbons found in geologic formations, such as rock strata. Most petroleum is a fossil fuel, formed from the action of intense pressure and heat on buried dead zooplankton and algae. Technically, the term petroleum only refers to crude oil, but sometimes it is applied to describe any solid, liquid or gaseous hydrocarbons.
Composition of PetroleumPetroleum consists primarily of paraffins and naphthenes, with a smaller amount of aromatics and asphaltics. The exact chemical composition is a sort of fingerprint for the source of the petroleum.