A thermodynamic model developed for CO2 and H2S solubilities in aqueous MDEA solution is extended to cover CO2 and H2S solubilities in aqueous DIPA solution, aqueous sulfolane-DIPA solution, and aqueous sulfolane-MDEA solution. The model makes use of the 2009 version of the electrolyte NRTL model for liquid phase activity coefficient calculations and the PC-SAFT equation of state for vapor phase fugacity coefficient calculations. The NRTL binary parameters for the molecule-electrolyte pairs required for the H2O-DIPA-CO2 ternary and the H2O-sulfolane-DIPA-CO2 quaternary are regressed against the solubility data of CO2 in aqueous DIPA solution and aqueous sulfolane-DIPA solution, respectively. The NRTL binary parameters for the molecule-electrolyte pairs required for the H2O-DIPA-H2S ternary and the H2O-sulfolane-DIPA-H2S quaternary are regressed against the solubility data of H2S in aqueous DIPA solution and aqueous sulfolane-DIPA solution simultaneously. The NRTL binary parameters for the electrolyte-electrolyte pairs involved in the H2O-DIPA-CO2-H2S quaternary are regressed against the solubility data of the acid gas mixtures in aqueous DIPA solution. Likewise, the NRTL binary parameters for the sulfolane-electrolyte pairs required for the H2O-sulfolane-MDEA-CO2 quaternary and the H2O-sulfolane-MDEA-H2S quaternary are regressed against the solubility data of the acid gases in aqueous sulfolane-MDEA solution. The predicted enthalpies of acid gas absorption are compared favorably with the literature data available for the H2O-DIPA-CO2 system, the H2O-DIPA-H2S system, and the H2O-sulfolane-MDEA-CO2 system. (C) 2011 Elsevier B.V. All rights reserved.