The extended UMR-PRU (eUMR-PRU) model is used in this work to describe the solubilities of H2S and mixed acid gases (H2S + CO2) in aqueous monoethanolamine (MEA) and methyldiethanolamine (MDEA) solutions. Moreover, the effect of methane on the solubility of CO2 in aqueous MDEA solutions is examined. For the chemical equilibrium description, the equations of the mole fraction-based equilibrium constants are solved simultaneously with mass balance and electroneutrality equations. For the vapor-liquid equilibrium calculations, the eUMR-PRU model is applied after the determination of the missing interaction parameters. The eUMR-PRU model is compared to other widely used models, namely, the Kent-Eisenberg model and the electrolyte NRTL model. It is shown that the eUMR-PRU results are in satisfactory agreement with the experimental data and similar to those obtained by other models.