Reported here is a novel technique, based on inverse gas chromatography (IGC), to measure the three-dimensional solubility parameters of nonionic surfactants-nonyl phenol ethoxylates-with different ethylene oxide chain lengths at two different temperatures. These solubility parameters can then be used to characterize the relative oil and water affinities of the surfactant. The three-dimensional solubility parameters of these surfactants were determined on the basis of the measured interaction parameters and known three-dimensional solubility parameters of the solvents (probe molecules) used in the IGC experiments, In particular, it was assumed, based on the regular solution theory, that the occurrence of a zero or negative interaction parameter is evidence of thermodynamic compatibility of the particular probe and surfactant. The three-dimensional solubility parameters of the surfactant are obtained by averaging the corresponding values of the compatible low-molecular-weight probe substances. In this way, combination of the lattice model of solutions (which allows negative enthalpies of solution) and the solubility parameter theory (which accounts for endothermic solutions only) is not required, As a result, measured negative interaction parameters are not a stumbling block for obtaining Hildebrand and three-dimensional solubility parameters. The method described is applicable to measurement of three-dimensional solubility parameters of all materials. Surfactants were used here as a convenient illustration only.