A number of chemical parameters has been proposed and sometimes adopted as time passes, with the aim of assess identity and quality of fatty substances. In this paper, the advancement of knowledges about fatty substances composition is stressed as highlighted by analytical instrumentation developments. Furthermore, a number of acquisition are rewieved, as they become available by hyphenation of analytical instrumentation, as LC-GC, LC-LC and LC-LC-GC. New trends in analytical evaluation of olive oils deal with application of NMR as well as Raman spectroscopy and Near Infrared Reflectance analysis. The main problem of fatty substances is oxidation: a number of recent knowledges are reported, dealing with products of oxidation of sterols, catalysed by heat and light, photo oxidation products and thermo oxidation products of sterols have been studied and identified. This lead to explain the possibility of newly formed sterenes in refined oils: their structure characterised by one more double bond in the rings is in good agreement with the dehydration of oxysterols. The antioxidative properties of a number of natural substances can be studied by means of stressed conditions, as realised in the Rancimat test or in the presence of free radicals at lower temperature, as realised in the crocine test. Xenobiotic, too, can occasionally be present in fatty substances, among these, polycyclic aromatic hydrocarbons have attracted the attention of several researchers since twenty years ago, significative advancement of analytical instrumentation in this field, too, admits their evaluation and study of their occurrence in fatty foods.
