A pore-network model is developed to study the liquid water movement and flooding in a gas diffusion layer (GDL), with the GDL morphology aken into account. The dynamics of liquid water transport at the pore-scale and evolution of saturation profile in a GDL under realistic fuel cell operating conditions is examined for the first time. It is found that capillary forces control liquid water transport in the GDL and that liquid water t moves in connected clusters with finger-like liquid waterfronts, rendering concave-shaped saturation profiles characteristic of fractal capillary fingering. The effect of liquid coverage at the GDL-channel interface on the liquid water transport inside GDL is also studied, and it is found that liquid coverage at the GDL-channel interface results in pressure buildup inside the GDL causing the liquid water to break out from preferential locations. (C) 2007 Elsevier Ltd. All rights reserved.