The fatty acid composition of the seed oils of Thespesia populnea and cotton variety SG-747 (Gossypium hirsutum) were studied to identity their 17-carbon fatty acids. With a combination of chemical derivatization, gas chromatography, and mass spectrometry, 8-heptadecenoic acid, 9-heptadecenoic acid, and 8,11-heptadecadienoic acids were identified in both oils. Additionally, traces of 10-heptadecenoic acid were identified in the T. populnea oil. Although these odd-carbon number fatty acids are present in only minor amounts in cottonseed oil, they make up about *2 % of the fatty acids in T. populnea seed oil. The identification of these acids indicates that fatty acid a-oxidation is not restricted to cyclopropene fatty acids in these plants, but also occurs with unsaturated fatty acids. Combined with malvalic acid (generally accepted as being formed by a-oxidation of sterculic acid), *7 % of the fatty acids in T. populnea seed have under gone a-oxidization. The results should help clarify the composition of T. populnea seed oil, which has been reported inconsistently in the literature.