The results of research of thermal-oxidative stability of motor oils of different underlying fundamentals. Proposed indicators for classification of engine oils, including a potential resource, the temperature of the beginning of the transformation process and the critical temperature. Based on the studies, it is shown that the application of the proposed method for the classification of motor oils allows you to get additional information about their quality, including indicators such as: potential resource, the temperature at which transformations in oil begin and the critical working temperature.