The conjugated linoleic acids (CLAs), octadeca-10E,12Z-dienoic and octadeca-11Z, 13E-dienoic acids, have been identified by 2D NMR spectroscopy in simple fatty acid mixtures. Unequivocal assignments for reporter resonances in the 13 C NMR spectra of these molecules are given. NMR assignments for the olefinic carbons of octadeca-8E,10Z-dienoic acid have also been obtained, along with full 13 C assignments for the octadeca-9,11-dienoic acids (ZE, ZZ and EE isomers). These data have been used to interpret the 13 C NMR spectrum of a complex CLA mixture, allowing the olefinic carbon chemical shifts of all isomers of 7,9 to 11,13 CLAs to be deduced. A method for the quantification of these compounds by 13 C NMR is described, demonstrating the utility of 13 C NMR spectroscopy in the analysis of complex CLA mixtures.