Fossil energy is a type of energy resource derived from ancient plants and animals that have been naturally converted into combustible materials through biological and geological processes over millions of years. Examples of fossil energy sources include coal, oil, and natural gas. This energy source has a lower level of efficiency than renewable energy sources, due to its limited and finite nature, and its extraction, refinement, and usage can cause significant environmental damage. It is becoming increasingly necessary for society to transition to more sustainable, renewable energy sources in order to shift away from fossil energy sources that have been linked to the climate crisis.

See also: fossil fuel, fossil carbon, fossil hydrocarbons, nuclear power, nuclear fuel