The paper presents the results of a thorough analysis of selected physicochemical parameters of engine oils at the end of their useful life, based on the oil change intervals assumed by vehicle users. Twelve samples of used Castrol Edge 5W/30 synthetic oil and five samples of used Castrol Magnatec 10W/40 semi-synthetic oil were tested. The Eralytics's ERASPEC OIL device was used for the assessment of the following parameters: degree of oxidation, degree of nitration, degree of sulfonation, water content, glycol content, total base number (TBN), total acid number (TAN) and kinematic viscosity at 40°C and 100°C. The research was conducted on the basis of the ASTM E2412-10 standard. The results regarding the parameter limit exceedances have also been presented in the paper. For both synthetic and semi-synthetic oils, the exceedance of kinematic viscosity measured at 40°C was particularly striking. In fourteen samples (out of seventeen tested), at least one exceedance of the limit value (out of nine analyzed) has been observed.