Isothermal vapor-liquid equilibria at 333.15 K and 353.15 K for four binary mixtures of benzene + nonane, toluene + o-xylene. m-xylene + sulfolane and o-xylene + sulfolane have been obtained at pressures ranged from 0 to 101.3 kPa over the whole composition range. The Wilson, NRTL and UNIQUAC activity coefficient models have been employed to correlate experimental pressures and liquid mole fractions. The non-ideal behavior of the vapor phase has been considered by using the Peng-Robinson equation of state in calculating the vapor mole fraction. Liquid and vapor densities of these solutions were measured by using two vibrating tube densitometers. The excess molar volumes of the liquid phase were also determined. The P-x-y phase behavior indicates that mixtures of m-xylene + sulfolane, o-xylene + sulfolane and benzene + nonane present large positive deviations from the ideal solution and belong to endothermic mixings because their excess Gibbs energies are positive. (C) 2009 Elsevier B.V. All rights reserved.