The Sprow–Prausnitz equation is employed to describe quantitatively the nature, properties and compositions of surface layers in binary liquid mixtures. Wide variety application, high accuracy, and required parameters that are normally easy to obtain are advantages of Sprow–Prausnitz equation compared to other methods. Bulk mole fraction, surface molar area and surface tension of pure component are necessary inputs for this equation. UNIFAC group contribution method is also applied into account for the non-ideality of the bulk liquid as well as that of the surface layer. The average relative error obtained from the comparison of experimental and calculated surface tension values for 154 binary systems with different surface tension behaviors show the model has good accuracy in comparison with other predictive equations. In addition to find more information about surface structure of binary mixtures, surface tension of binary mixtures has been studied using extended Langmuir model (EL)
