The air/water partition coefficients of carboxylic acids, Kw, especially those of high molecular weight, are very difficult to determine directly. Values of Kw can be obtained by an indirect method as Kw = K/P where K is an air/solvent partition coefficient and P is the corresponding water/solvent partition coefficient. In the present method, gas-liquid chromatographic data and water/solvent partition data are used to obtain 'descriptors' of carboxylic acids that can then be used to determine the required K, P, and thus Kw values. These are reported for all the 24 n-alkyl carboxylic acids from formic acid to n-tetracosanoic acid, and for seven branched chain alkyl carboxylic acids. There is good agreement with literature values of Kw, where available, although the present data on the n-alkyl carboxylic acids is much more self consistent than the literature data.