Various noble metal compositions are used for three-way catalyst applications. The most typical composition contains platinum and rhodium at various loadings and ratios. Recently palladium and rhodium compositions have received considerable attention by automobile companies.The strengths and weaknesses of the various noble metal use strategies have been widely discussed. Unfortunately, the content for much of the discussion has been based on information generated in the early to mid-1970s with catalysts of relatively simple formulation when compared to today's higher technology products.The present study compares the relative durability performance of modern platinum/rhodium and palladium/rhodium catalysts of identical loading under a variety of aging and evaluation conditions. These conditions were chosen to simulate some of the operating conditions encountered in U.S. and European driving applications. The results of the study also illustrate the progress made in developing high performance palladium/rhodium catalyst technologies.