  We develop constitutive equations for multi-component, multi-phase,
macro-scale flow in a porous medium exposed to temperature-, composition-, and
pressure -gradients. The porous medium is non-deformable. We define the
pressure and the composition of the representative elementary volume (REV) in
terms of the volume and surface averaged pressure and the saturation, and the
respective driving forces from these variables. New contributions due to
varying porosity or surface tension offer explanations for non-Darcy behavior.
The interaction of a thermal and mechanical driving forces give thermal
osmosis. An experimental program is suggested to verify Onsager symmetry in the
transport coefficients.
