Fossil fuels (oil, coal, and natural gas) are non-renewable sources of energy formed in the earth over the past 550 million years, typically from the remains of marine microorganisms and plants. Sealed off from oxygen and put under ever-increasing amounts of heat and pressure, this organic matter undergoes a thermal breakdown process that ultimately converts it to hydrocarbons.

When fossil fuels are burned, they release pollutants which contribute to global warming and acid rain.

The United States gets 81% of its total energy from fossil fuels. They heat our homes, run our vehicles, power industry and manufacturing, and provide us with electricity. Eventually, the degree to which we depend on fossil fuels will have to decline as they are non-renewable resources, as the difficulty and cost of tapping remaining reserves increase, and as the effect of their continued use on our planet grows more critical.  

The share of U.S. total energy consumption that originated from fossil fuels has fallen from its peak of 94% in 1966 to 80% in 2018.