found a reduction of 42.86 and 21.71% in the levels of polyunsaturated fatty acids in olive and sunflower oils, respectively, after 15 h of frying. The decrease in linolenic and a-linolenic acids may represent a loss of nutritional value, because they are essential fatty acids and are not synthesized by the human body. The results regarding stearic, arachidic, behenic and eicosenoic fatty acids showed that they remained virtually unchanged in most samples. Palmitic and oleic acids showed a slight increase in most samples (Table 3). The fatty acid composition values of the initial oils are close to those presented by Gunstone (1996), who established soybean oil values of 15, 22 and 61% of saturated, monounsaturated, and polyunsaturated fatty acids, respectively. There was a significant increase in saturated and monounsaturated fatty acids and a reduction in polyunsaturated fatty acids, regardless of the addition or absence of antioxidants (Table 4). However, significant changes in the fatty acid composition were mainly found in treatments without added antioxidants.