ABSTRACTCorn oil, hydrogenated corn oil and corn oil margarine were compared on the basis of fatty acid composition and triglyceride structure, including configurational isomerism of unsaturated fatty acids. Hydrogenated corn oil contained trans unsaturation and positional isomers not naturally found in corn oil. The β‐position of triglycerides of hydrogenated corn oil was 85% occupied by trans octadecenoic acids (trans‐18:1); that of corn oil was 70% occupied by linoleic acid. The proportion of cis octadecenoic acids (cis‐18:1) in the β‐position of the triglycerides was distinctly less in the hydrogenated corn oil than in corn oil, indicating a hydrogenation and/or a geometrical isomerization of cis‐18:1 to trans‐18:1 preferentially in the β‐position, as compared with the α‐positions. Chemical composition of corn oil margarine was intermediate between that of corn oil and that of hy