Vapour pressures of (benzene + 1,1,2,2-tetrachloroethane (TCANE)), or (benzene + tetrachloroethene (TCENE)) at nine temperatures between 283.15 and 323.15 K were measured by a static method. The reduction of the vapour pressures to obtain activity coefficients and excess molar Gibbs energies was carried out by fitting the vapour pressure data to the Redlich-Kister polynomial according to Barker's method. A comparative analysis about the thermodynamic behaviour of both systems is performed, taking into account the resonance effect in tetrachloroethene. (C) 2004 Elsevier B.V. All rights reserved.