A pore network model of the gas diffusion layer of PEMFCs is presented. Unlike previous attempts based on cubic lattices, this model has a random 3D architecture based on Delaunay tessellations to represent the pore space and Voronoi tessellations to represent the fiber structure. Very few input parameters are required to generate the model. Fiber diameter is specified, the number of pores per unit volume is adjusted to achieve a desired porosity, and the network is scaled to impart some in-plane vs. through-plane anisotropy. The resulting network possesses physical properties (such as pore and throat size) and transport properties (such as effective diffusivity tensor) that are in excellent agreement with available values. Capillary pressure curve simulations were compared with mercury and water injection data. Good agreement with the former was attained if the equivalent throat diameter was used in the calculation of entry pressures. Comparisons to water injection data were very poor unless the converging-diverging geometry of the throat was considered, in which case very close agreement was achieved. A relatively simple analytical equation was used to account for the throat geometry and its use is strongly recommended over the traditionally used equation for cylindrical capillary tubes. (C) 2013 The Electrochemical Society. All rights reserved.