Distribution of reactant gases in polymer electrolyte membrane fuel cells (PEMFCs) plays an important role in current density distribution, temperature distribution, and water concentration. This claim is bound up with the local consumption of reactants and local transport of water through the membrane. Problems like flooding or drying of the membrane which may reduce the life time of the MEA can be associated to the non-uniformity of the above parameters. Optimization of the flow-field design is an applicable idea to prevent these undesired events. Channel to rib ratio is a remarkable factor of flow field design for increasing the performance and life time of PEM fuel cells. It is believed that decreasing the rib width will increase hydrogen concentration at the anode side, but near zero rib width value might crush the MEA layer at high pressure contact areas which is not appropriate. So defining an optimum channel to rib ratio is inevitable in fuel cell design. In this paper seven flow fields are analyzed and fuel cell performance is investigated at the optimum channel to rib ratio. The effects of flow fields on current density, mass fraction of reactant gases, water distribution and flooding are numerically verified. Moreover, the effects of stoichiometry, pressure and temperature on the cell performance are assessed. Ultimately the best flow field design is introduced according to the polarization curve. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.