The empirical nature of the well-known Ergun equation for prediction of the permeability of granular materials inhibits the straightforward generalization to other geometries of the pore space and non-Newtonian effects of traversing fluids. In this paper the results are discussed of a pore-scale model that can be regarded as qualitative and quantitative proof of the Ergun equation. The pore-scale model has superior adaptive capabilities and also allows investigation of the porosity dependence of the empirical coefficients of the Ergun equation. Some advantages, based on physical grounds, of the pore-scale model are outlined. (c) 2008 Elsevier Ltd. All rights reserved.