The performances of two gas-channel designs of bipolar plates were investigated by numerical simulations and experimental in-cell tests. The experimental study examined the performances of two gas-channel geometries and materials under cathode and anode flooding conditions. Design 1 consisted in straight-parallel channels with graphite monopolar plates. On the other hand, Design 2 was made of a double-channel serpentine flow field pattern with stainless steel monopolar plates. Design 1 did not provide a uniform flow distribution over the gas diffusion layer, so liquid water was accumulated in certain regions. The flow velocity in Design 2 was higher and produced more uniform electrical current distributions than the straight-parallel channels design. This design, using 304 SS plates, diminished the effect of the electrical resistance related to the mass transfer rate.