The influence of energy-supply structure on emission-reduction costs for SO2 is outlined and evaluated. For this purpose, eight representative countries have been selected for analysing impacts due to different energy scenarios varying in final energy demand, fuel prices, assumed CO2-emission reduction, and country-specific factors. We identify and quantify emission-reduction potentials of a restructuring of national energy systems and energy-conservation measures, as well as impacts on emission-reduction costs. These results are country-specific and are therefore important for ongoing negotiations of international protocols on reductions of SO2.