Abstract. We consider a charged porous material that is saturated by two fluid phases that are immiscible and continuous at the scale of a representative elementary volume. The wetting phase for the grains is water and the non-wetting phase is assumed to be an electrically insulating viscous fluid. We use a volume averaging approach to derive the linear constitutive equations for the electrical current density as well as and the seepage velocities of the wetting and non-wetting phases at the scale of a representative elementary volume. These macroscopic constitutive equations are obtained by volume-averaging Ampère's law together with the Nernst-Planck equation and the Stokes equations. The material properties entering the macroscopic constitutive equations are explicitly described as a function of the saturation of the water phase, the electrical formation factor, and parameters that describe the capillary pressure function, the relative permeability function, and the variation of electrical conductivity with saturation. New equations are derived for the streaming potential and electro-osmosis coupling coefficients. A primary drainage and imbibition experiment is simulated numerically to demonstrate that the relative streaming potential coupling coefficient depends not only on the water saturation, but also on the material properties of the sample as well as the saturation history. We also compare the predicted streaming potential coupling coefficients with experimental data from four dolomite core samples. Measurements on these samples include electrical conductivity, capillary pressure, the streaming potential coupling coefficient at various level of saturation, and the permeability at saturation of the rock samples. We found a very good agreement between these experimental data and the model predictions.