The document discusses biogas as a transport fuel. It can currently only be used where it is produced, so there is a need to make it transportable by upgrading the quality. Upgrading involves removing carbon dioxide, hydrogen sulfide, and water vapor through processes like water absorption or molecular sieves. This produces upgraded biogas that has similar properties to natural gas and can be used in natural gas vehicles. The document then provides background on biogas production and use in Europe as well as methods for upgrading raw biogas quality to meet fuel standards.