The surface tensions of 100 aqueous and 200 non-aqueous binary solutions are correlated by Shereshefsky model and excellent results are obtained. The average percent deviations are about similar to 1.8% for aqueous and similar to 0.56% for non-aqueous binary solutions. The free energy change in the surface region is calculated and is used to obtain the excess number of molecular layers in the surface region. Furthermore, the model is used to derive an equation for the standard Gibbs energy of adsorption. Where experimental data is available for the standard Gibbs energy of adsorption, the agreement between the calculated and the experimental data is found to be very good. (c) 2005 Elsevier Ltd. All rights reserved.