GDL in a PEM Fuel Cell is a porous medium which helps in transporting the reactant and the liquid water to/from the catalyst layer. Simulations were carried out on a three-dimensional porous structure containing four layers of fibers arranged in criss-cross direction. The liquid water movement through the structure was simulated with different fiber-fluid interface contact angles, e.g. as 130, 120 and 110°, indicating different extents of hydrophobicity. As the hydrophobicity increased, the liquid water moved vertically upwards without spreading along the length of the fiber, as observed in case of contact angle of 130 and 120° in contrast to the contact angle of 110°. Pressure changed significantly with time and also across the air-water interface, while the variation within the liquid continuum was fairly small. This is an abstract of a paper presented at the 19th International Congress of Chemical and Process Engineering and 7th European Congress of Chemical Engineering (Prague, Czech Republic 8/28/2010-9/1/2010).