This work investigated the hydrocarbon degradation and depletion of the anti-wear additive zinc dialkyldithiophosphate (ZDDP) in several used marine motor oils using high-resolution nuclear magnetic resonance (NMR). The article presents research results showing that during engine operation a number of characteristics of motor oil change: degree of aromaticity, ratio of methyl/methylene groups, and composition of phosphorus-containing additives. The possibility of determining oil using the NMR spectrum lines of antiwear additives has been demonstrated. For anti-wear additives containing phosphorus, such as ZDDP and molybdenum dialkyldithiophosphate (MoDDP), 31P NMR has been found to provide both depletion rates and insight into the wear mechanism of the additives. The high efficiency of using the high-field NMR spectroscopy method for studying fresh and destruction of used marine motor oils has been demonstrated. 1H, 13C and 31P NMR studies show the presence of changes in motor oil caused by the accumulation of products of its decomposition, degradation and decomposition of additives during engine operation. The ability of the NMR radiospectroscopy method to monitor additive depletion is analyzed, which is apparently one of the most difficult problems in used oil analysis. A characteristic feature of the NMR spectra of all used oils is line broadening caused by the presence of metal wear particles. It is characteristic that the broadening of the 13C NMR lines for waste oils is significantly less than the lines broadening in the NMR spectra of protons. In the 13C NMR spectrum of used oil, an increase in the intensity of the line from aromatic hydrocarbons is observed, i.e. as the degree of oil degradation increases, the content of aromatic compounds increases. The results of the study of fresh and used motor oils obtained in this work are new. They can be used to create a system for monitoring the quality of motor oils and for diagnosing engine malfunctions using used oil.