The paper describes the study on relationship between the engine lubricate oil quality and fluorescence phenomenon. In order to determine the Excitation-Emission spectra (EEMs) of oil samples, a spectrofluorometer combined with an optical fiber system were applied. Two methods of fluorescence measurement: when oil diluted in non-fluorescent solvent (n-hexane) is placed in the quartz-cuvette inside the spectrofluorometer, and when oil sample is placed outside the spectrofluorometer (then EEMs is measured through the optical fiber sensor) were utilized to analyze the shape of EEMs of lubricate oil. Moreover in the second case of measurement, the optical fiber sensor was placed at an angle of 45 degrees to the oil surface, similarly above the oil surface and beneath the oil surface directly submerged in oil. Preliminary measurement results presented in this paper – on one hand – indicate diversity in the shape of EEMs depending on the method of fluorescence measurement, on the other hand – indicate possibility to measure fluorescence of oil directly in engine lubricate oil circuit.