An experimental investigation was conducted to test the use of non-conventional analyses for determining the actual level of oxidative and hydrolytic degradation of edible oils and fats. For this purpose three extra-virgin olive oils, three refined oils recovered from in-oil preserves, and three refined fats extracted from margarines were considered. Besides the determination of the free fatty acids, the peroxide value, the spectrophotometric constants, the fatty acid composition, and the trans isomers content – prescribed by the EC Regulations – the high performance size-exclusion chromatography of polar compounds – separated from oils and fats by silica gel column chromatography following an IUPAC method – was carried out to separate and quantify the main classes of oxidation and hydrolysis substances. The results obtained show that the routine analyses can enable an effective measurement of quality only for extra-virgin olive oils. On the other hand, for determining the actual degree of the oxidative and hydrolytic degradation of oils and fats subjected to treatments requiring high temperatures (refining, hydrogenation, etc.) the HPSEC (High Performance Size Exclusion Chromatography) analysis of polar compounds can be successfully used. The determination of trans isomers contributes to the assessment of the quality of different oils.