Isothermal vapor-liquid equilibrium (VLE) at 333.15 K and 353.15 K for four binary mixtures of benzene+toluene, benzene+N-methylformamide, toluene+m-xylene and toluene+N-methylformamide have been obtained at pressures ranged from 0 kPa to 101.3 kPa. The NRTL, UNIQUAC and Wilson 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 Soave-Redlich-Kwong equation of state in calculating the vapor mole fraction. Liquid and vapor densities were also measured by using two vibrating tube densitometers. The P-x-y diagram and the activity coefficient indicate that two mixtures of benzene + toluene and toluene + m-xylene were close to the ideal solution. However, two mixtures containing N-methylformamide present a large positive deviation from the ideal solution. The excess Gibbs energy in the benzene + toluene mixture is negative indicates that it is an exothermic system. (C) 2009 Elsevier B.V. All rights reserved.