FTIR spectroscopy has been used to examine the spectral changes taking place in the polar fraction of thermoxidized virgin olive oil and compared to those changes occurring in the neat oil and the nonpolar fraction. It was demonstrated that examination of the polar fraction provides additional and substantially better information of the chemical changes taking place as oxidation proceeds because this fraction concentrates the oxygenated compounds formed. Of particular interest is the enhancement of the OH component of the spectrum (3600-3200 cm(-1)) as well as tertiary alcohol formation (~1167 cm(-1)), including the region associated with epoxides. Time course spectral changes for neat virgin olive oil and its polar and nonpolar fractions are illustrated, compared, and contrasted, demonstrating that the interpretation of neat oil spectra is greatly enhanced by fractionation and may in fact be a preferred means of studying thermoxidation processes.