Biofuels encompass a variety of fuels that are, in some way, created from renewable energy sources (called biomass). Ethanol, which is derived from corn, is a biofuel. Biodiesel, made from vegetable oils or recycled greases, is a biofuel. Experiments have been conducted on algae, solid waste, and animal fats, among others. Biofuels can be used alone to power vehicles, but they're most often used as additives.