The UNIFAC model is extended to mixtures of ionic liquids consisting of the imidazolium cation and the hexafluorophosphate anion with alkanes, cycloalkanes, alcohols and water. Two new main groups, the imidazolium and the hexafluorophosphate groups, are introduced in UNIFAC. The required group interaction parameters between these groups and the existing UNIFAC main groups, CH2, OH and H2O, are determined by fitting binary liquid-liquid equilibrium and infinite dilution activity coefficient experimental data. The predictive capability of the extended UNIFAC model is examined against experimental data for vapour-liquid equilibrium, liquid-liquid equilibrium and activity coefficients at infinite dilution of binary and ternary systems containing 1-alkyl-3-alkyl'-imidazolium hexafluorophosphate ionic liquids, alkanes, cycloalkanes, alcohols and water. The results indicate that UNIFAC is a reliable model for phase equilibrium predictions in mixtures containing this type of ionic liquids. (C) 2009 Elsevier B.V. All rights reserved.