Fossil energy sources, including oil, coal and natural gas, are non-renewable resources that formed when prehistoric plants and animals died and were gradually buried by layers of rock. Over millions of years, different types of fossil fuels formed -- depending on what combination of organic matter was present, how long it was buried and what temperature and pressure conditions existed as time passed.

Today, fossil fuel industries drill or mine for these energy sources, burn them to produce electricity, or refine them for use as fuel for heating or transportation. Over the past 20 years, nearly three-fourths of human-caused emissions came from the burning of fossil fuels.

The Energy Department maintains emergency petroleum reserves, ensures responsible development of America’s oil and gas resources and executes natural gas regulatory responsibilities. In addition, scientists at the Energy Department’s National Labs are developing technologies to reduce carbon emissions and ensure fossil energy sources play a role in America’s clean energy future.