The purpose of the article was to analyze the foaming tendency of engine oils used under excessive operating conditions. To achieve this end, foaming characteristics were determined for 23 oil samples in three measurement sequences. Foaming tendency was measured using the ASTM D 892 standard method, which consists in assessing foaming tendency of the liquid and foam stability. The cars used in the tests were uniform in terms of brand, type and operating conditions. The relationship between the mileage of the cars tested and the volume as well as stability of foam in used engine oils were presented using scatter plots with regression lines, correlation coefficient and 95% confidence interval. Based on the obtained results it was found that foaming tendency for new oils is characterized by high variability. The strongest foaming tendency at 24°C and 93°C (Sequence I and II) was observed for two out of five oil groups. Statistically significant differences were found between mileage and foaming tendency/foam stability for individual oils tested.