Molecular diffusion in multicomponent systems has been the subject of many theoretical studies. Problem with many of these approaches is that they violate material balance constraint and lead to non-physical predictions. Theories by Zielinski and Hanley, Alsoy and Duda have been tested and negative concentrations are observed for the balancing third component. The proportionality assumption between the self-diffusivity and molecular weight (M) made by Price and Romdhane in their generalized model eliminated the problem. However such a restriction is not applicable for high polymer systems were diffusivity is proportional to M^-2. The proportional flux model introduced by Nauman and Savoca takes care of the problem without the need to constrain the self-diffusivity to the molecular weight.