A fuel is a substance that can be converted by combustion or other process so that useful energy is released. The most common process is combustion, but it can also be another chemical reaction. In order for a fuel to be useful, the energy must be economically and technically feasible. The energy of a fuel must also be stored for a reasonable period of time, and often the energy must also be produced so that it can be converted into work.
With regard to fuel for cars, the longest has been the most common with petrol or diesel fuels. There are alternatives to biofuels such as biogas and ethanol (alcohol) primarily for passenger cars as well as RME and HVO, which is biodiesel. RME produced by chemical refining of rapeseed oil using methanol is used primarily as fuel in buses and lorries. HVO, a diesel fuel produced from vegetable oils, can be used by all diesel cars. Then we also have electricity, right now, there are cars that can be powered by electricity that is most on the Swedish market.