Radioactive oils were run in a laboratory V8 engine to determine the effects of viscosity and volatility on oil consumption. Using a tritium tracer method, very precise oil consumption rate measurements were obtained.The consumption rates of 14 test oils, blended from two crude sources, were measured at different engine speed and load conditions. To compare test oils run on different days, a computerized multiple regression analysis was required to compensate for daily variations in oil consumption. Another computer-aided statistical analysis related oil consumption rates to viscosity and volatility. Both hypothetical and empirical equations were used. Field tests were run to obtain a correlation with the laboratory test.Volatility was found to be the most important single characteristic affecting oil consumption. Smaller and less consistent consumption differences between oils were found in the field tests than in the laboratory engine.