Water transport within Proton Exchange Membrane Fuel Cell (PEMFC) is investigated by systematic measurements of the water transport coefficient, defined as the net water flux across the membrane divided by the water production. It is recorded for various operating conditions (current density, gas stoichiometry, air inlet relative humidity, temperature, pressure) in a fuel cell stack fed by dry hydrogen. The measurement of the water transport coefficient shows that a significant fraction of water is collected at the anode while water is produced or injected at the cathode. Moreover, in usual operating conditions, liquid water is present at the cell outlet not only in the cathode but also in the anode. Contrary to the electrical performances, ageing has no influence on the water transport coefficient, which allows the comparison between data collected at different periods of the fuel cell lifetime. From this comparison, it was found that the hydrogen flow rate, the amount of vapor injected at cathode inlet, and the temperature are the main parameters influencing the water transport coefficient. It is shown that air and hydrogen stoichiometry present significant effects on water transport but only through these parameters. (c) 2009 Elsevier B.V. All rights reserved.