Fossil fuels fossil fuel energy Fossil energy sources fossil energy type of fossil fuel formed U.S. Dept. of Energy: Fossil energy.gov/science-innovation/energy-sources/fossil fossil energy fossil fuels Department of Energy – Fossil Fuels These sources are Fossil fuels Fossil fuels U.S. Department of Energy: Fossil fossil fuels Department of Energy: Fossil Fuels fossil energy fossil energy U.S. Department of Energy, Energy.gov -- Fossil fuels Fossil fuels Fossil fossil fuel oil Department of Energy – Fossil Fuels energy.gov/science-innovation/energy-sources/fossil Fossil fuels fossil Fossil Fuels Energy.gov: fossil fuels Department of Energy - Fossil Fuels fossil fuels Department of Energy – Fossil Fuels Department of Energy – Fossil Fuels fossil energy Department of Energy1 fossil fuel fossil fuels fossil fuels. Department of Energy – Fossil Fuels