History matching of unsteady immiscible displacement experiments performed on model porous media reveals that nonequilibrium capillary pressure and relative permeability functions are sensitive to the dominating flow pattern. As the capillary number increases, the network displacement pattern changes gradually from invasion percolation cluster to stable displacement. For primary drainage, the capillary pressure and relative permeability curves are increasing functions of the capillary number. The dependence of the relevant macroscopic parameters on the capillary number is consistent with power laws derived from scaling arguments of gradient percolation theory, which describes the growth of the displacement front. The material coefficient of the thermodynamic theory of capillary pressure changes mildly with fluid saturation and is a decreasing function of the capillary number.