The problem of controlling quality of motor oils in the course of their development, production and operation in cars is actual. We propose using a few drops of oil and surface plasmon resonance refractometer “Plasmon-71” (developed in Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine) to determine the degree of oil contamination and make a decision to replace it (Fig.1, 2). The measurements take only 5 minutes, method is very easy, fast and sensitive! Such measurements can be carried out consecutively throughout the year and make a decision to replace the oil with its significant contamination. The developed technique allows to investigate perspective compositions of motor oils, as well as wear of motor parts.