Biogas is the gaseous product of anaerobic digestion (decomposition without oxygen) of organic matter. It is typically made up of 50-80% methane, 20-50% carbon dioxide, and traces of gases such as hydrogen, carbon monoxide, and nitrogen. Biogas is sometimes called swamp gas, landfill gas, or digester gas. When its composition is upgraded to the required level of purity (and compressed or liquefied), biogas can be used as an alternative vehicle fuel in the same forms as conventionally derived natural gas: compressed natural gas (CNG) and liquefied natural gas (LNG).
An estimated 12,000 vehicles are being fueled with upgraded biogas worldwide, with 70,000 biogas-fueled vehicles predicted by 2010. Europe has most of these vehicles. Sweden alone reports that more than half of the gas used in its 11,500 natural gas vehicles is biogas. Germany and Austria have established targets of 20% biogas in natural gas vehicle fuel. In the United States, biogas vehicle activities have been on a smaller scale. One example includes a landfill in Whittier, California that fuels vehicles with CNG derived from the landfill. The total cost of the CNG facility was approximately $1 million. At full production the facility is capable of producing clean fuel at an equivalent gasoline cost of $0.50 per equivalent gallon of gas.