The given introduced paper deals with determination of contamination, content of elements, change of composition and stability against the oxidation of motor oils. This work is aimed at chaining the individual properties of engine oil in dependence on the use of oil in traffic. Results show, that properties of engine oils do not depend only on the time of use but they also depend on other factors, such as state of the vehicle, the way of driving the vehicle, and the condition of maitenance.