It is a heavy dark liquid, consisting of many different hydrocarbon compounds. Crude oil is extracted from the ground and fractionated into its components by volatility in an oil refinery. Some of the main products distilled from crude oil are:
Geologistss have deduced that fossil fuels are the remains of huge amounts of algal material that was laid down millions of years ago, and altered in form under high temperatures and pressures. Layers of buried plant material tend to produce coal or lignite.
A minority belief is that petroleum is synthesized naturally by unspecified underground processes, slowly rising towards the surface for our use.