What are fossil fuels made of?

Fossil fuels are made from the organic remains of decomposing plants and animals. These fuels are found in the Earth’s crust and contain carbon and hydrogen, which can be burned for energy. Coal, oil, and natural gas are examples of fossil fuels. While coal is a material usually found in sedimentary rock deposits where rock and dead plant and animal matter are piled up in layers, oil is originally found as a solid material between layers of sedimentary rock, like shale. This material is heated in order to produce the thick oil that can be used to make gasoline.

Source: National Geographic