Accurate knowledge of gas solubility is necessary for the development of processes involving ionic liquids (ILs) and gases. In this work, a group contribution approach is used to predict the phase behavior of CO2 + IL systems based on the statistical associating fluid theory (SAFT-gamma) as proposed by Lymperiadis et al. The IL molecule is divided into groups of CH3, CH2, cation head, and the anion. The SAFT-gamma parameters of CO2 + imidazolium-based ionic liquids with either [PF6], [BF4] or [Tf2N] anions are optimized to experimental data. The ability of the model to describe the phase behavior of these systems is demonstrated within a temperature range of 313.15-353.15K and pressures up to 100 bars. Moreover, by using the optimized group parameters, the performance of the model is examined by predicting equilibrium data of some CO2 + IL systems not included in the optimization database. The results show good agreement with experimental data. (C) 2012 Published by Elsevier B.V.