A thermodynamic model was used to estimate enthalpy of solution of carbon dioxide (CO2) in methyldiethanolamine (MDEA) aqueous solutions. The model was based on a set of equations for chemical equilibria, phase equilibria, charge, and mass balances. Non-ideality in the liquid phase was taken into account by interaction parameters fitted to (vapor + liquid) equilibrium data. The enthalpies of solution of CO2 were derived from the model using classical thermodynamic relations and were compared to experimental values obtained in previous works. (C) 2009 Elsevier Ltd. All rights reserved.