Biofuel is any fuel derived from an organic material that is not fossilized like coal or petroleum. Common sources of biofuel grown for the U.S and European markets are corn, soybeans, flaxseed and rapeseed. Biofuel can appear in solid, liquid, or gas form. It is used to produce heat or electricity, or to power machinery using burners, broilers, generators, internal combustion engines, turbines or fuel cells. Biofuel is a renewable energy, but there is some controversy that it is not sustainable due to the harvesting of biomass and the byproducts produced during the burning of biofuels.