Fourier transform infrared spectroscopy (FTIR) coupled to chemometrics techniques was used to investigate high quality motor oils samples adulterated with lower quality oils, like used oils and standard oils. The results showed that Partial Least Squares (PLS) models based on infrared spectra were a suitable analytical method for predicting adulteration of high quality motor oils in the concentration range from 0% to 36% (w/w), with prediction errors lower than 3% (w/w). Partial Least Squares Discriminate Analysis (PLS2-DA) gave good classification results with 100% correct class prediction, in the spectral range of 1800-600 cm(-1) and concentration range of 0-20% w/w for the two tested oil adulterants in their binary mixtures with the high quality oil. The proposed method can be employed for quality monitoring and control and rapid screening analysis of adulterated motor oils. (C) 2012 Elsevier Ltd. All rights reserved.