A test program was conducted using a wide variety of laboratory oil and fuel performance test procedures in order to compare effects of unleaded fuel versus leaded fuel. These tests included standard industry-accepted procedures such as Sequences IIB, IIIC, and VC, as well as procedures unique to the Lubrizol laboratory. Preliminary results which are reported in this paper will be subjected to verification in future tests. Initial results have indicated that unleaded fuel is more severe than leaded fuel with respect to varnish deposits, full throttle octane requirement increase, exhaust valve seat wear, and wear of certain other engine components. Results have also shown unleaded fuel to be less severe on rust deposits, spark plug fouling, and oil thickening due to oxidation. Sludge deposits were only slightly less severe with unleaded fuel, and the differences compared with leaded fuel are not believed to be significant. The use of exhaust gas recirculation in selected test procedures has shown that suitably formulated crankcase oils can counteract possible detrimental engine deposits resulting from this anticipated means of oxides of nitrogen control.