The relation between the performance of a self-humidifying H₂/O₂ polymer electrolyte membrane fuel cell and the amount and distribution of water as observed using ¹H NMR microscopy was investigated. The integrated ¹H NMR image signal intensity (proportional to water content) from the region of the polymer electrolyte membrane between the catalyst layers was found to correlate well with the power output of the fuel cell. Several examples are provided which demonstrate the sensitivity of the ¹H NMR image intensity to the operating conditions of the fuel cell. Changes in the O₂(g) flow rate cause predictable trends in both the power density and the image intensity. Higher power densities, achieved by decreasing the resistance of the external circuit, were found to increase the water in the PEM. An observed plateau of both the power density and the integrated ¹H NMR image signal intensity from the membrane electrode assembly and subsequent decline of the power density is postulated to result from the accumulation of H₂O(l) in the gas diffusion layer and cathode flow field. The potential of using ¹H NMR microscopy to obtain the absolute water content of the polymer electrolyte membrane is discussed and several recommendations for future research are provided.