  We study average flow properties in porous media using a two-dimensional
network simulator. It models the dynamics of two-phase immiscible bulk flow
where film flow can be neglected. The boundary conditions are biperiodic which
provide a means of studying steady state flow where complex bubble dynamics
dominate the flow picture. We find fractional flow curves and corresponding
pressure curves for different capillary numbers. In particular, we study the
case of the two phases having equal viscosity. In this case we find that the
derivative of the fractional flow with respect to saturation is related to the
global pressure drop. This result can also be expressed in terms of relative
permeabilities or mobilities, resulting in an equation tying together the
mobilities of the two phases.
