The solubilities of H2S in aqueous solutions of diisopropanolamine (DIPA) and in aqueous mixtures of DIPA and piperazine (Pz) have been measured. The molality of DIPA was fixed at 2.96 m, and the concentration of Pa was (1.20 or 1.80) m. Experiments were carried out at (40, 60, and 80) degrees C over the pressure range (19 to 1554) kPa. For modeling of the DIPA + Pz + H2S + H2O system, the electrolyte cubic square well (eCSW) equation of state (EOS) (Haghtalab, A.; Mazloumi, S. H. Fluid Phase Equilib. 2009, 285, 96-104) was applied to predict the total and partial pressures of H2S over aqueous solutions of DIPA, Pz, and DIPA + Pz using only the interaction parameters, k(ij), of the H2S + H2O system. The reasonable agreement of the eCSW EOS and experimental results demonstrates the good accuracy of the eCSW EOS for thermodynamic modeling of the solubilities of acid gases in aqueous alkanolamine solutions.