During exploitation the oil gradually changes its physical and chemical properties. The causes of these changes in oil are physical-chemical and tribological processes in the system during operation, the conditions under which oil performs its function and the conditions in the system environment. To the degradation of the oil during operation comes mainly due to the oxidation of hydrocarbons at high temperatures. Temperature is one of the most important factors that influence on the degree of oxidation, whether it is industrial or motor oil. Oxidation products are peroxides as well as alcohols, ketones, aldehydes, carboxylic acids. These products react with each other and form a high molecular, insoluble compounds in the oil, what leads to changes of oil characteristics, with direct effect on the functionality of the lubricant. In this paper is examined the effect of temperature on the process of chemical degradation of oil. Also is determined the influence of base oil and oxidation inhibitor on the chemical stability of the oil.