It is well established that drainage in porous media can be characterized by two non dimensional numbers: the capillary number, Ca, and the viscosity ratio, M. Both quantities are useful to distinguish which force (viscous or capillary) is governing the fluid displacement behavior This information is summarized in the Ca-M phase diagram. The Ca-M phase diagram is strongly dependent Upon fluid properties and the porous medium morphology and wettability. Experimental evidence Suggests that the morphology of the porous medium has an important role in the behavior in the fluid displacement. In this work. Ca-M phase diagram of fuel cell diffusion media layer (DM) is explored using a pseudo-Hele-Shaw experimental setup. This phase diagram will be explored together with the characteristic pressure curves of each displacement type. This Ca-M phase diagram will provide a fundamental resource for Understanding the dynamics of the diffusion process and transport characteristics taking place inside of the DM as well as a characterization method for DMs. (C) 2009 Elsevier B.V. All rights reserved.