In this research the performance of sesame seeds and sweet almond oils was analyzed used as lubricants in preventive wear testing (AW) in a four-ball tribometer. The impedance spectroscopy technique was used in the frequency range of 0.2 to 2000 kHz as a tool for diagnosis of the state of the oils. Impedance measurements were performed on the oils before and after wear testing. The results obtained were compared with the behavior of two mineral oils with different viscosity, oils 255 and 360, used as lubricants under the same conditions. From the test results of wear testing it was determined that the sweet almond oil has greater lubricity compared with sesame oil and therefore the impedance spectra of fresh and used oil haven't presented any significant differences. From the comparison of the impedance spectra of sesame and mineral base oils, it was established that the higher the degree of wear, the greater the difference between the impedance spectra of fresh oils and used ones. Finally, based on the results it was showed that the impedance spectroscopy technique can be used to differentiate between vegetable and mineral oils.