The paper aims to the prediction of interfacial properties of binary mixtures using only pure component interfacial properties and bulk-properties of the mixture, like phase equilibria. This approach follows strictly the basic idea from Van der Waals. In principle, this goal can be reached by the application of the density gradient theory in combination with an equation of state. This paper focuses on the thermodynamic description of the phase and the surface properties for binary systems, if a supercritical component, like nitrogen or carbon dioxide (CO2), is present in the mixture. Whereas nitrogen can be treated as nonpolar component, carbon dioxide has a strong quadrupole moment. Using PCP-SAFT-EOS in combination with the density gradient theory the prediction of the surface tensions of mixtures close to experimental data is possible. (C) 2010 Elsevier B.V. All rights reserved.