Presented are advantages and disadvantages of direct and indirect methods of oil evaporation losses determination. Reviewed is an indirect method, based on predominant evaporation of light fractions from oil and corresponding reduction of saturated vapours pressure. Developed is a procedure of losses determination, which realizes abovementioned method with application of UODS-1 unit and "Procedures for measuring of saturated oil vapours pressure", methrologically approved by MBI. It is noted, that accuracy of the new method under convergence and reproduction conditions is higher, than required by State Unified Standard 1756, and its application is expedient not only technically, but also economically