Operating parameters, material properties and flow field geometry have a deterministic role on the water storage and distribution within the flow channels and porous media in a fuel cell. However, their effects are not yet precisely understood. In this study, extensive neutron imaging experiments were conducted to visualize and quantify the amount of liquid water in the fuel cell channels and diffusion media as a function of inlet gas flow rate, cell pressure and inlet relative humidity. A seven-channel parallel flow configuration PEFC was used to isolate these parameters from flow field switchback interaction effects. The neutron imaging experiments were performed at different inlet gas flow rates, operating cell pressures and inlet relative humidities. At each operating condition, the distribution of liquid water in the diffusion media under the lands, and in or under the channels was obtained. Furthermore, at three different cell pressures (0.2 MPa, 0.15 MPa and 0.1 MPa), liquid water distribution and quantification was obtained. The liquid water mass in the cell decreased with increasing pressure for over-humidified anode inlet conditions. Comparison of the fuel cell performance with the total liquid water mass in the cell indicates a non-monotonic relationship between liquid water content and performance. Furthermore, cell performance was highly sensitive to incremental changes in the membrane liquid water content. (c) 2006 Elsevier B.V. All rights reserved.