Formation of Fossil Fuels Source: TesTeach A fuel is a material that stores chemical potential energy. Coal, petroleum, and natural gas, are known as fossil fuels. Fossil fuels contain energy that came from the sun. In fact, the sun is the major source of energy for most of Earth's processes. When ancient animals and plants died, the chemical potential energy they had stored was trapped within them. This is the chemical potential energy that is found in coal. Use of Fossil Fuels Fossil fuels…