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This paper describes the results of a research program to evaluate the effect of lowering zinc dithiophosphate (ZDDP) content on engine oil performance. The automative industry is concerned that engine oil composition may have an adverse effect on exhaust catalytic converter efficiency and has therefore called for more research to develop engine oils that will promote catlyst/engine oil compatibility. An apparently simple solution is to reduce ZDDP content to a level that allows satisfactory catalyst efficiency. The effects of lowering the ZDDP content have been evaluated in terms of wear, oxidation and bearing corrosion performance. It has been demonstrated that in laboratory engines and rig tests by quantifying the influence of lubricant composition on performance, engine oils can be formulated at lower phosphorous levels (0.08% wt) to meet the performance needs of modern passenger cars in the United States, Europe and Japan.