An electrolyte equation of state based on Redlich Kwong Soave EOS is applied to the representation of the equilibrium properties of the water-CO2-diethanolamine system in the 298-366.5 K temperature range. In this work we have developed a model which is able to represent the liquid phase speciation as well as the CO2 solubility in the amine solutions. For this purpose the database used for the parameters determination consists of solubility data as well as Henry's constants and speciation data including experimental concentrations of molecular CO2 and of carbamate. The need of such speciation data is shown by a comparison of the speciation results obtained and those predicted using models from the literature based only on the data treatment of experimental VLE values. (C) 2013 Elsevier B.V. All rights reserved.