An original gas chromatography/mass spectrometry method for quantifying trace amounts of ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid) is detailed. Data are presented on trace amounts of ricinoleic acid found in several common vegetable oils and oils extracted from common oil seeds: e.g., ca. 30 ppm in commercial olive oil was the lowest amount; and ca. 2,690 ppm in oil extracted from cottonseeds was the highest amount.