The effect of the anode and cathode flow field depths on the performance of a single cell Direct methanol fuel cell (DMFC) of 45 cm(2) active area were experimentally investigated. Double serpentine flow fields (DSFFs) with varying channel depth namely, 0.2, 0.4, 0.6, 0.8, and 1 mm but with fixed channel and rib width each of 1 mm on both anode and cathode were designed, fabricated, and tested. The experimental study involved measurement of pressure drops across anode and cathode flow field plates, polarization, and carbon dioxide concentration measurements at various current densities. The mass transport at both anode and cathode were found to increase with increase in pressure drop across the flow field on account of reduced channel depth from 1.0 to 0.4 mm at all current densities. However, further decrease to a channel depth of 0.2 mm was found to be counter-productive with different phenomena operating on either side viz., increased CO2 slug length on the anode flow channel and increased methanol crossover on the cathode side. Hence, the maximum performance for DMFCs was observed for a channel depth of 0.4 mm on anode and cathode flow fields. A decrease in flow field channel depth at cathode was found to increase the methanol crossover due to convective mass transfer effect.