COSMO-RS, a general, very fast, and easy-to-use methodology for the a priori prediction of thermodynamic data of liquids, is applied to six binary mixtures for which recent accurate experimental vapor-liquid and liquid-liquid equilibria data are available (Giles, N. F.; Wilson, G. M. J. Chem. Eng. Data 2000, 45, 146). The quality and applicability of COSMO-RS in the prediction of activity coefficients and vapor pressures are thus demonstrated. It is shown that COSMO-RS is an alternative to structure-interpolating group contribution methods because it is independent of experimental data and generally applicable.