Group contribution methods for the calculation of an activity coefficient such as UNIFAC (universal factorial activity coefficient) currently do not take into account sterical effects. Consequently one of the major deficiencies of such methods is their inability to resolve isomeric systems and their often insufficient accuracy for systems including molecules of very different size. In this paper an approach is presented by which sterical information can be implemented into those methods by means of a modified group vector space (GVS) procedure. (Wen, X.; Qiang, Y. Group Vector Space method for estimating melting and boiling points of organic compounds. Ind. Eng. Chem. Res. 2002,41, 5534-5537.) Exemplary calculations with UNIFAC/GVS underline the potential of this new approach resulting in a perspective for substantially improved group contributions methods with a wider range of applicability and even more reliable predictive performance.