coal
Energy produced by types of coal.

oil
Petroleum products (primarily crude oil and its derivative fuel oils).

natural-gas
Hydrocarbon gas liquids (HGL) that occur as gases at atmospheric pressure and as liquids under higher pressures including Natural gas (C5H12 and heavier), Ethane (C2H6), Propane (C3H8), etc.

nuclear
Energy produced from the cores of atoms (i.e., through nuclear fission or fusion).

wind
Energy produced from moving air.

solar
Energy produced from the sun (i.e., solar radiation).

geothermal
Energy produced from heat within the earth.

hydropower
Energy produced from flowing water.

biofuel
Liquid fuels produced from biomass feedstocks (i.e., organic materials such as plants or animals).

unknown
The energy source is unknown.

other
An energy source that is not listed.
