Fuels are used to heat and cool buildings, cook food, power engines, and produce electricity.
Some fuels occur naturally and others are artificially created.
Such natural fuels as coal, petroleum, and natural gas are obtained from underground deposits that were formed millions of years ago from the remains of plants and animals. These fuels, which are called fossil fuels, account for about 90 per cent of the energy people use today. Synthetic fuels can be made from fossil fuels, certain types of rock and sand, and biomass. Biomass is the name given to such replaceable organic matter as wood, garbage, and animal manure that can be used to produce energy. Some synthetic fuels are made from chemicals.