The development of an extended Peng-Robinsort equation of state is described, which allows for the consideration of salts in calculations for the high-pressure vapor + liquid phase equilibrium. The extension employs two terms: a Debye-Huckel and a Margules term. The new equation is applied to systems with carbon dioxide, water, methanol, acetic acid, sodium chloride, and sodium acetate. For the adjustment of the nonionic and ionic interaction parameters experimental data of the phase equilibrium of binary and ternary system are used. The extended Peng-Robinson equation of state is then used to predict the phase equilibrium of quaternary systems of the type carbon dioxide + water + organic solvent + salt. (c) 2004 Elsevier B.V. All rights reserved.