In this study, literature review about fatty acid compositions of triacylglycerols, which are the main components of many food products, was carried out. The literature shows that octadecenoic acids, both trans and cis isomers, are the major fatty acids found in food products. The main source of these isomers are hydrogenated and ruminant fats. Also, isomers are formed during the refining of oils, mainly at the deodorization stage. The aim of the study was to correlate the oxidative stability of cis and trans octadecenoic fatty acids. Fatty acid methyl esters of oleic and elaidic acids as well as partially hydrogenated oils (olive and Canola oils) were used in the study. The following two accelerated tests used for studying the oxidative stability of fats were used: differential scanning calorimetry (DSC) method and Schaal oven test. The results showed that the geometric configuration of octadecenoic fatty acids of triacylglycerols influenced the oxidative stability of fats. Fats containing higher quantities of trans isomers of these fatty acids were more stable. In case of oleic and elaidic acid methyl esters, the difference in oxidative stability was not significant.