The fractionation of marine-oil triglycerides according to their degree of unsaturation was achieved on silica gel thin layers with 8% silver nitrate (w/w). Under the optimum conditions, cod-liver and whale oils were reproducibly separated into seven and six fractions, respectively. The fatty acid compositions of the fractions obtained from cod-liver and whale oils were further studied by gas-liquid chromatography. The following was found in both oils: Saturated and monoenoic acids were not only abundant in their corresponding fractions, but also comprised about two-thirds of the fatty acids in the more unsaturated fractions. Instead, polyenoic fatty acids of similar degrees of unsaturation predominated only in the particular fraction which corresponded to their number of double bonds. Thus, the distribution of fatty acids of varying degrees of unsaturation among marine triglycerides is not random.