The description of two-phase flow in porous media is traditionally based on Darcy's equation. Accordingly, effective permeabilities to each phase are expected to be smaller than absolute permeabilities, and also they determine each phase mobility. A typical behaviors such as oil relative permeabilities values larger than one, can be obtained during depressurization experiments of heavy oil saturated porous media when the data is analyzed under the conventional Darcean approach. Such an unconventional behavior is physically possible considering that the Darcean approach disregard several flow sources such as viscous coupling derived from the momentum transfer between the phases. Oil relative permeabilities larger than one, which actually are apparent values, could represent one of the most convincing evidence of the role of viscous coupling on two-phase flow in porous media. In this paper we present experimental indication of such unconventional behavior and show how it can be properly understood when taking into account the viscous coupling contribution on each phase mobility. Pore network simulations are used to complement the analysis and evaluate the effect of the capillary number on the transport parameters involved in the generalized flow equations. (c) 2007 Elsevier Ltd. All rights reserved.