The Penn State Microoxidation Tester coupled with gel permeation chromatography and clay column adsorption techniques has been demonstrated to be an effective tool to provide semi-quantitative analysis for automotive crankcase lubricant deterioration. This test simulates engine piston-cylinder zone high-temperature thin-film conditions. Oxidative behavior of a series of ASTM Sequence IIID hot engine test reference oils (with unknown base stocks and additive packages) has been found to be comparable to and consistent with that of a model fluid formulated with a good quality conventionally refined heavy neutral and a simple additive system composed of phenyl alpha naphthylamine and zinc dialkyldithiophosphate. Further simplification of the test procedure for evaluating varnish and deposit formation tendencies proves to be an effective aid in discriminating base oils as well as compounded fluids with a minimum of analytical equipment. High temperature evaluations of a number of commercial multigrade engine oils reveal the slight advantage of synthetic over conventional mineral base oils both in terms of oxidation resistance and volatility loss.