Anaerobic digestion for biogas production is a promising renewable energy technology whichcan be used to achieve environmental goals set in the European Union and other regions. Thereare however many improvements that can still be made to the process. Furthermore, there arealternative energy conversion processes that compete for some of the substrates used inanaerobic digestion. Energy efficiency could therefore be a tool for measuring and comparingthe performance of biogas plants. This study suggests a method for calculating energyefficiency of the biogas plant so that it is comparable to other processes. Two examples ofexisting biogas plants in Sweden have been selected for the efficiency assessment by using themethod proposed in this paper. The results are compared between the plants to assess thefurther potential of improvement.