A thermodynamically consistent model was developed for representing vapor-liquid equilibria in the acid gas (H2S, CO2)-alkanolamine-water system. The model accounts for chemical equilibria in a rigorous manner. Activity coefficients are represented, with the Electrolyte-NRTL equation treating both long-range ion-ion interactions and local interactions between all true liquid-phase species. Both water and alkanolamine are treated as solvents. Adjustable parameters of the Electrolyte-NRTL equation, representing short-range binary interactions, were fitted on binary and ternary system VLE data. Calculated H2S and CO2 equilibria are in good agreement with most of the reported experimental data for aqueous solutions of a single acid gas in monoethanolamine (MEA) and diethanolamine (DEA) in the temperature range 25–120 °C. Without fitting additional parameters, representation of experimental equilibria for mixtures of H2S and CO2in aqueous solutions of MEA or DEA is good.