Biogas is a gaseous biofuel formed by anaerobic decomposition of organic matter. Biogas can be extracted from a wide variety of materials, for example, on wastewater treatment plants, on landfill sites, on farms where biodegradable material is present or collected or from slaughter waste. The raw gas consists mainly of hydrocarbon methane (50-75 %) and carbon dioxide (25-50 %) as well as minor amounts of impurities such as hydrogen sulphide, hydrogen sulfide and ammonia. In order to be used in vehicles, the gas needs to be refined so that the methane content increases and the other substances decrease.
Gas cars have, in principle, common petrol engines that are supplemented with a separate gas fuel system. Special pressure vessels are used where the gas is compressed to a maximum of about 200 atmospheres (206 kg/cm²) pressure. Pure biogas reduces CO2 emissions by about 80 % compared to gasoline, and other emissions by about 70 %. Gas cars have about 1-4 crowns lower mileage compared to gasoline cars, but it is shorter gas coverage compared with gasoline. Petrol stations are expensive to build, about 150 stations in Sweden, and it is higher purchase costs for the vehicles compared to petrol vehicles. Worth noting is that about 40 % of all vehicle gas fueled in Sweden is fossil natural gas.