Compounds of fossil or organic origin made up of molecular chains of carbon and hydrogen, which are essential as fuels for most means of transport. They are usually a mixture of many types of molecules. Typical liquid hydrocarbons used as fuels are diesel and gasoline. Their use is convenient because of a high energy content per unit mass. Liquid hydrocarbons are either obtained by fractional distillation from crude oil or produced by Fischer-Tropsch synthesis from natural gas or syngas.