Biofuel is any solid, liquid or gas fuel which is made from biomass, or living material. In contrast to fossil fuels, biofuels utilize materials formed by things that are or have recently been living.
A number of biofuels are becoming increasingly important on the energy landscape. For example, ethanol, a biofuel made from corn, is commonly added to gasoline as an extender; more recently, vehicles are becoming commercially available that can run on straight ethanol. Biodiesel is made from plant oils, including oils that have been used in the cooking process, to make a fuel which can be used directly in standard diesel engines.
Methane can be captured from fermentation processes such as composting and sewage treatment and can be burned as natural gas for heat or electricity production. Solid biofuels come in many forms, including processed wood pellets and corn pellets.
Biofuels are widely considered to be part of the solution to diminishing petroleum reserves; however when used as fuels they do contribute carbon dioxide to the atmosphere, and in many cases arable land that formerly was used to produce food has been converted to growing feedstock for biofuels.