In this work, a modified perturbed hard sphere chain (PHSC) equation of state has been applied to the calculation of acid gas (CO2, H2S) solubility in ionic liquids. The proposed equation of state is a combination of the PHSC equation of state and a polar term. The polar contribution is based on the segment approach which is expected to give accurate results for long chain molecules such as ionic liquids. By using polar and association terms, the specific interactions between molecules have been taken into account. The calculated results for ionic liquid densities are in good agreement with the experimental data, and average deviation between calculated and experimental data is less than 0.14%. The solubility of CO2 and H2S in various ionic liquids has been correlated using just one temperature-dependent binary interaction parameter over wide ranges of temperature and at pressures ranging from 0.1 to 100 MPa. For binary systems, absolute average deviations of calculated gas solubilities are less than 2.4%. The capability of the proposed model has then been assessed by prediction of solubility behavior for the ternary H2S/CO2/[C(4)mim][PF6] system. (C) 2011 Elsevier B.V. All rights reserved.