Selectivity factors and partition coefficients of ethylene carbonate and the (ethylene carbonate + sulfolane) solvent mixture for the separation of benzene or toluene from (benzene or toluene + n-heptane) are obtained from the experimental + equilibrium data for ternary mixtures of (ethylene carbonate + benzene or toluene + n-heptane) at temperatures of (303 15 and 313 15) K and quaternary mixture of (ethylene carbonate + sulfolane + benzene + n-heptane) at 303 15 K The composition of liquid phases at equilibrium was determined by gas-liquid chromatography and the results were correlated with the UNIQUAC and NRTL activity coefficient models The parameters of the models were evaluated and reported The phase diagrams for the mixtures studied are presented and the correlated tie line results have been compared with the experimental results The comparisons indicate the applicability of the UNIQUAC and NRTL activity coefficients model for (liquid + liquid) equilibrium calculations of the mixtures studied. (C) 2010 Elsevier Ltd All rights reserved.