Samples of engine oils of CC or CD API grades contaminated with edible rapeseed oil (2-10%) have been oxidized in the cell of a pressure differential scanning calorimeter (PDSC). The PDSC experiments were carried out under 1400 kPa oxygen pressure at 190 degrees C. From the resulting PDSC exotherms their extrapolated onset and peak maximum times have been determined and compared with results obtained under the same conditions for engine oils without addition of vegetable oil. The presence of rapeseed oil in engine oils drastically decreases their resistance to oxidation.