Multicomponent high-resolution 1 H and 13 C NMR analysis has been employed for the purpose of detecting and quantifying a wide range of fatty acids (as triacylglycerols or otherwise) in encapsulated marine cod liver oil supplements. The 1 H NMR technique provided quantitative data regarding the docosahexaenoic acid content of these products, which serves as a valuable index of fish oil quality, and a combination of both 1 H and 13 C spectroscopies permitted the analysis of many further components therein, including sn -1 monoacylglycerols, sn -1,2 and -1,3 diacylglycerol adducts, together with a range of minor components, such as trans -fatty acids, free glycerol and cholesterol, and added vitamins A and E. The identities of each of the above agents were confirmed by the application of two-dimensional 1 H-1 H spectroscopies. The NMR techniques employed also uniquely permitted determinations of the content of nonacylglycerol forms of highly unsaturated (or other) fatty acids in these products (i.e., ethyl esters), and therefore served as a means of distinguishing "natural" sources of cod liver oils from those subjected to chemical modification to and/ or supplementation with synthetic derivatives such as ethyl docosahexaenoate or eicosopentaenoate. The analytical significance and putative health effects of the results acquired are discussed.