The thermo-oxidation engine oil simulation test (TEOST)® MHT protocol was used to generate information on deposits and the formation of polar volatile organic compounds. Fourier transform IR (FTIR) spectroscopy was then used to analyze the level of oxidation in recovered TEOST® used oil as well as in the collected volatiles. Data was generated comparing different antioxidant systems in molybdenum-containing and molybdenum-free low-phosphorus engine oil formulations. The results show a surprising difference in deposits, volatiles, and carbonyl oxidation based on the presence or absence of molybdenum and also based on the type of antioxidant system selected. The amount of volatiles produced in the TEOST® is related to well-established oxidation mechanisms and also explains specific oxidation processes sometimes seen in Sequence III engines. A mathematical definition of antioxidant effectiveness or “robustness” is proposed that combines TEOST® deposits and volatiles measurements with FTIR carbonyl oxidation measurements. These results strongly suggest that an analysis of TEOST® used oils and volatiles may provide valuable information regarding oxidation in other bench tests as well as potentially in fired engines. Presented at the STLE Annual Meeting in Las Vegas, Nevada May 15-19, 2005 Review led by Cyril Migdal