A rapid and accurate method for determining group contributions to liquid phase activity coefficients for a binary system of groups from measurements of net retention volumes by gas-liquid chromatography has been developed. Group contributions determined by this method for four different pairs of groups at a number of different temperatures were used to calculate 110 equilibrium compositions for 11 different binary systems of nonelectrolytes. These were compared with experimental equilibrium data and indicated an overall absolute average deviation of 5.9%. Of the 1 10 deviations, 19 were greater than 10% and of these, three were greater than 30%. It also appears from these studies that the partial residual energy of mixing at infinite dilution is a constant for a given solute in a homologous series of solvents.