In this paper various biogas systems based on waste materials have been analysed from an environmental point of view. The analyses are based on Swedish conditions using a systems analysis approach from an energy and life cycle perspective. The biogas produced is used as a transportation fuel replacing petrol in light-duty vehicles. The overall aims are to quantify the potential environmental effects when current waste handling and transportation fuel systems are replaced. A general conclusion is that the indirect environmental benefits (e.g. reduced emissions of ammonia and methane, and nitrogen leaching) from altered handling of organic waste materials and land-use may often significantly exceed the direct environmental benefits achieved when biogas replaces petrol (e.g. reduced emissions of carbon dioxide and air pollutants). Such indirect benefits are seldom considered when biogas is evaluated from an environmental point of view. However, the environmental impact from different biogas systems can vary significantly due to factors such as the waste materials utilised, different reference systems being replaced, and local conditions.