The gas diffusion layer (GDL) is a crucial component as regards the water management in proton exchange membrane fuel cells. The present work aims at discussing the mechanisms of water transport in GDL on the cathode side using pore network simulations. Various transport scenarios are considered from pure diffusive transport in gaseous phase to transport in liquid phase with or without liquid–vapor phase change. A somewhat novel aspect lies in the consideration of condensation and evaporation processes in the presence of a temperature gradient across the GDL. The effect of thermal gradient was overlooked in previous works based on pore network simulations. The temperature gradient notably leads to the possibility of condensation because of the existence of colder zones within the GDL. An algorithm is described to simulate the condensation process on a pore network.