This paper focuses on the development of an on-line measurement method for siloxanes and other biogas trace compounds impeding the energy utilisation of biogas, as well as the main gas components, methane and carbon dioxide. The method is based on gas chromatography and FT-IR-analysis. The level of siloxane, hydrogen sulphide and halogens in biogas generated in a number of landfills and digesters in Finland is also presented and factors affecting the concentrations discussed. Generally, the level of biogas trace compounds hampering electricity production was lower than those measured at comparable sites in Central Europe and the US. Moreover, the paper discusses the significance of on-line monitoring of siloxane in connection to biogas-to-electricity applications and points out with activated carbon as an example the benefits of on-line siloxane measurement in the control of siloxane removal technology.