The purpose of the study was to measure and assess differences in concentrations of wear metals occurring in used engine oils. The concentrations of the following trace elements have been assessed: Cr, Cu, Fe, Mn, Mo, Ni, Pb. The research was carried out using the HDMaxine analyzer produced by XOS, operating on the basis of high definition X-ray fluorescence (High Definition X-ray Fluorescence - HDXRF). The capacity of the engine was elaborated as the factor differentiating the content of trace elements in oils. Only the vehicles whose owners used fully synthetic oils (viscosity grade 5W30, 5W40) or 10W40 semi-synthetic oils were included in the test. The engine oils analyzed represented seven different brands. The samples were acquired during oil change services from passenger cars of different manufacturers. As many as 40 samples of used oil were tested: 23 of them were collected from passenger cars with engine capacity up to 1400 cm3 (Group I) and the other 17 from passenger cars with engine capacity equal to or above 1500 cm3 but not exceeding 2000 cm3 (Group II). The analysis of the results showed that the oil samples collected from the engines with a capacity equal to or above 1500 cm3 were characterized by a higher average concentration of the following elements: Cr, Fe, Ni and Pb. On the other hand, in the oil samples collected from the engines with a capacity equal to or below 1400 cm3 only Cu showed higher values. Manganese and molybdenum remained at similar levels for both groups. The obtained results, providing information on the changes in the concentration of wear metals, can be useful in determining the patterns behind the engine wear processes for various engine capacities.