Crude oil is a thick, dark liquid found in rocks under the ground or the sea bed. It is a mixture of many different hydrocarbons, which are compounds containing only hydrogen and carbon atoms. Most of the hydrocarbons in crude oil are alkanes. Crude oil formed over millions of years from the remains of ancient plankton that were buried in mud and exposed to heat and pressure.
Crude oil is the main source of hydrocarbons. It is separated into useful fractions by fractional distillation. Many of these hydrocarbons are burned as fuels, for example petrol, diesel and kerosene.
Crude oil is also a feedstock for the petrochemical industry. A feedstock is a raw material that is used as the starting point to make other chemicals. The petrochemical industry uses hydrocarbons from crude oil to make products such as polymers (plastics), solvents, lubricants and detergents.