Conventional and high oleic sunflower oils as well as 50% mixture of both of them were heated at different temperatures under well-controlled conditions. Total polar compounds, the main groups of polar glycerides, total polar fatty acids, the mair groups of polar fatty acids and the loss of initial fatty acids were quantitated. The most outstanding results demonstrated the primacy of the formation of glyceridic polymerization compounds during heating at high temperatures. After transesterification of the samples dimeric fatty acids was the most significant group of compounds obtained. As expected, linoleic acid was preferentially involved in the formation of polar fatty acids, although the participation of oleic acid became very important at low concentration of linoleic acid. 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