In the present work an extended UNIFAC group contribution model is used to calculate activity coefficients in solutions containing alcohols, water. carboxylic acids. esters, alkanes and aromatic hydrocarbons. The limiting expressions for the association contribution to the activity coefficients at infinite dilution are presented and discussed. A new set of interaction parameters between associating and non-associating functional groups is reported. This set of parameters is applied in the association model to predict vapor-liquid, liquid-liquid equilibrium and infinite dilution activity coefficients. (C) 2004 Elsevier B.V. All rights reserved.