In this paper we consider multicomponent mass transport in porous media for non-dilute solutions. This process is described by coupled, nonlinear transport equations that must be spatially smoothed in order to be useful. This spatial smoothing, or upscaling, is achieved by the method of volume averaging for the case of negligible adsorption, desorption, and heterogeneous reaction. For pure diffusion, the results demonstrate that a single tortuosity tensor applies to the transport of all species. When convective transport is important, the process becomes much more complex and it is difficult to generalize about the behavior of the various dispersion tensors. (c) 2005 Elsevier Ltd. All rights reserved.