In this paper, a fluorescein solution is injected into the gas diffusion layer (GDL) of a PEM fuel cell to simulate water flow through the porous medium under flooding conditions. The effect of the GDL hydrophobic treatment is studied by analyzing the images obtained from fluorescence microscopy. The intensity of images is correlated to the liquid water content in the medium. As a result, three distinguishable patterns are recognized between the treated and untreated GDL samples. These patterns include: (1) initial invasion, (2) progression and (3) pore filling. Based on the flow characteristics, a pore-network model is developed and applied to unique network geometry with different hydrophobic fractions to study the effect of hydrophobicity on the flow configuration. It is shown that the model predicts the flow configurations which are qualitatively in agreement with the experimental observation. The model is then used to obtain saturation for samples with different hydrophobic fractions. The trend is in agreement with the results reported in the past. (C) 2013 Elsevier B.V. All rights reserved.