Abstract: The activity coefficients of benzene in infinitely dilute solution in fourteen solvents at 60°C have been evaluated by gas-liquid chromatography. The activity coefficients of the same systems have been calculated by means of a monomer-dimer solution model. Calculation showed that the experimental data could be predicated by this model.The activity coefficients of toluene, ethylbenzene, o-xylene, rn-xylene and p-xylene in infinitely dilute solution in four solvents at 60°C have been evaluated also by gas-liquid chromatography.By applying a monomer-monomer solution model, the solubility para-menters of these solvents have been calculated. The values of solubility paramenter for the same solvent with different solutes are constant within the experimental uncertainty,