This paper reviews empirical studies on the relationship between environmental and economic performance carried out with European data in order to derive conclusions with regard to their methodological comparability. Two types of research are analysed, namely (model) portfolio studies and multiple-regression-based studies. For each type two representative empirical studies are contrasted in order to establish methodological influences, as well as the importance of data availability. The review allows us to formulate a set of criteria to support improved research design in the future. These point to a strong need to develop further the methodology of studies on the relationship between environmental and economic performance.