The contents of P, S, Ca, Zn and Mo in 5 samples of fresh oil (before introducing to an oil sump), after the course of 3500 km as well as after the next 50 km after introducing 500 mL of extra fresh oil to the oil sump were detd. by using an analyzer operating on the basis of high resolution X-ray fluorescence spectroscopy. Supplementing the oil in the oil sump resulted in an increase of the content of the analyzed elements from 0.4% to about 7%.