Proton-exchange membrane fuel cells (PEMFC's) has recently been the focus of intense research and development for powering the next generation of road vehicles, for distributed power generation as well as for powering small portable devices such as cellular phones and laptop computers. A two-dimensional numerical model describing the phenomena of gas flows in channels in a fuel cell PEMFC is presented. The influence of inlet pressure of gases and Reynolds number on the distribution and consumption of reagents is investigated. The gas flow is assumed laminar, unsteady, non isothermal and incompressible, flow fields of the anode and cathode sides are modeled as straight channels. The equations of conservation of mass, momentum and species are developed. A program based on the finite volume method was performed to simulate the system of equations governing the phenomenon. The simulation results show that when increasing the inlet pressure it will improve consumption of reagents and give more homogeneous distribution. The results also show that when increasing the Reynolds number it will improve consumption of reagents. However, we observed a more homogeneous distribution for low Reynolds number.