The momentum transfer mechanism between the fluid and solid phases and the practical implications of such a mechanism are investigated for flow through porous media. The continuum-mechanical approach based on the volume averaged equations for multiphase systems is used for the analysis. The results show that the drag between the two phases is equal to the local pressure gradient and that this drag force causes particle movement and not the particulate stress. The pressure gradient identifies regions within the porous media with high drag. Alterations of these regions can change global flow rates in porous media. The resistance function, which is an inverse permeability, has meaning only when it is related to the magnitude of the momentum transfer, or drag, between the phases. If a functionality for the porosity is necessary, then it should depend on the pressure gradient, or, under negligible gravitational effects, the gradient of the particulate or effective intergranular stress.