A method, to determine the volatility of oils by thermal gravimetric analysis, is presented. Shown is that the loss of weight of mineral base oils, and blended engine oils, can be measured in a practical manner. The method correlates with the DIN 51581 standardized method. The effect of small changes in temperature of analysis, and purge-gas flow is described. The method, which makes use of an oil with known weight loss, has a repeatability of 5%, and has been used during the past three years by our company.