Fuels are materials that give off heat when they are burned. A fuel may be a solid, a liquid, or a gas. Fuels that come from the remains of living things are called fossil fuels. Wood, coal, natural gas and the liquid fuel petroleum are common fossil fuels. We are only going to discuss petroleum here.
Petroleum is formed within the crust of the earth.
It is also called crude oil. Scientists think that the bodies of prehistoric sea animals and plants became trapped in sediments. After millions of years, heat and pressure changed them into crude oil and natural gas. Crude oil and natural gas are usually found together in the crust of the earth. To get the oil and gas, it is necessary to drill into the earth's crust.