This study looks for the first time at the possibility of predicting the interfacial tension in mixtures without preliminary resource to their experimental data. For this purpose the quantitative global phase diagram (k1GPD)-based approach (GPDA), which needs only two or three key experimental points of one homologue for predicting the complete phase behavior in whole homologues series of binary systems, is combined with the gradient theory (GT) methodology. The resulting model is able to predict the data in satisfactory manner, although the increasing asymmetry between the compounds of the mixture probably affects the ability of GPDA to yield accurate predictions of phase equilibria and interface tension simultaneously. (C) 2003 Elsevier B.V All rights reserved.