Automobile manufacturers are increasingly obligated to reduce the greenhouse gas emissions of their vehicle fleets. In this paper a framework to analyze the reduction potential of the life cycle CO2 emissions of passenger cars is developed. It comprises nine sub-modules - including macroeconomic and microeconomic oriented modules. For each module relevant elements to be considered are presented. Within a short case study the framework is applied to analyze the reduction potential of the CO2 emissions of passenger cars. The achieved results are discussed with respect to different technical and policy measures available in the US and German market.