The results of a study of the thermal-oxidation stability of motor oils are presented. The experimental data were obtained and analyzed by means of regression analysis, and graphical dependencies were constructed that clearly demonstrate the reaction of the lubricant to changing environmental conditions and with the help of which it was established that it is possible to determine the temperature of the onset of oxidation processes and temperature conversions, as well as their critical temperatures. As a criterion for evaluating thermal-oxidation stability, a coefficient of thermal-oxidation stability is recommended, taking into account the optical density and volatility of the oil. It shows the effectiveness of the method of predicting the performance indicators of a lubricant among existing research techniques.