A detailed knowledge of the molecular structure of the individual triacylglycerols (TAG) is essential to the understanding of the biological, chemical, physical, and technological properties of fats and oils and the foodstuffs they comprise. To understand the mechanisms of reactions, such as hydrolysis, trans-esterification, or chemical and biological oxidation, “averaged” information on fatty acid distribution between different stereochemical positions of fats and oils is often not enough. It is of special importance to distinguish between the fatty acids esterified at the primary (sn-1 and sn-3) and secondary (sn-2) positions of glycerol.