A quick routine analysis has been established for quantitative determination of thirteen individual C18 trans fatty acids in both pressed and solvent extracted non-hydrogenated edible vegetable oils, using gas chromatography-mass spectrometer (GC MS) equipped with HP-88 capillary column following potassium hydroxide/methanol (KOH/MeOH) methylation. Based on optimization and appraisal of the characteristics of GC MS, thirteen C18 trans fatty acid methyl ester (FAME) standards were separated and verified in 23 mm, validation experiments were also conducted. The correlation coefficient was R-2 >= 0.99 in the linear range of each FAME. At the low, medium and high fortification levels, recoveries fell within 90-119%. The relative standard deviations were below 9% for all 13 FAMEs. Low limits of detection (0.001 -0.002 g/100 g) and quantification (0.002-0.007 g/100 g) were readily achieved. The content of C18 trans fatty acid isomers in pressed and solvent extracted oils were analyzed using this method. (C) 2015 Elsevier Ltd. All rights reserved.