The equation of motion for single-phase fluid flow through porous media is derived by rigorous analysis of forces acting upon fluid based on a control volume momentum balance approach. Resistive forces associated with pore Surface and pore throat are characterized by the capillary-orifice model of porous media. This analysis reveals deficiencies of previous efforts in deriving the generalized momentum equation. The present approach provides resolution to several issues, including porous media averaging of the pressure and shear-stress terms, effect of porous media heterogeneity and anisotropy, and threshold pressure gradient that must be overcome for fluid to flow through porous media.