A combination of Twitchell's lead salt separation procedure and reverse phase thin‐layer chromatography on Plaster of Paris plates has enabled easy separation and identification of C20‐C24 minor saturated acids in mustard seed oils. This has further demonstrated the inapplicability of Bellier's turbidity point test for mustard oils by showing the quantitative variation in the proportion of C20‐C24 acids naturally present in these oils. Expected augmentation of minor acid spots in chromatograms could be shown by adulteration with groundnut oil. The method can be adapted for the detection of adulteration of fats and oils. Copyright © 1967 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim