The thermal treatment of vegetable oils was studied by gel chromatography on packings of styrene-divinylbenzene copolymers. Unlike oils with a lower content of polyene acids, those with a high content of polyene acids contained a larger amount of higher oligomers of fatty acids. The gel chromatography of fatty acid methyl esters from heated oils allowed the determination of the ratio of intra- and intermolecular bonds arising by polymerization reactions. The results of determination of the iodine value of products were correlated with the data obtained by gel chromatography.