Hi,
A fossil fuel is a natural substance formed from the buried remains of ancient organisms that can be used as a source of energy. Fossil fuels formed over millions of years as heat and pressure from layers of sediment changed the decayed organic remains into materials such as coal and petroleum.
How are they made?
Fossils fuels are usually made of fossilized plant and animal remains from millions of years ago. The creation of fossil fuels—either oil, natural gas, or coal—from these fossils is determined by the type of fossil, the amount of heat, and the amount of pressure which they bore.
Hope it helps....
(by Benjemin)