A gaseous, liquid, or solid fuel that contains an energy content derived from a biological source. The organic matter that makes up living organisms provides a potential source of trapped energy that is beginning to be exploited to supply the ever-increasing energy demand around the world. An example of a biofuel is rapeseed oil, which can be used in place of diesel fuel in modified engines. The methyl ester of this oil, rapeseed methyl ester (RME), can be used in unmodified diesel engines and is sometimes known as biodiesel. Other biofuels include biogas and gasohol.