A unified PEMFC model, three dimensional steady state numerical mass transfer model for polymer electrolyte membrane fuel cell was developed for multi-parallel flow field (MPFF) channel design of bipolar plates. This model was developed to determine the effect of operating parameters such as humidification, temperature and pressure on the cell performance. Transport equations formulated under PEMFC conditions were solved using the commercial CFD software Fluent 5.5. In this paper, model results for effect of humidification are presented. These results indicate that as the humidification level in the cell increases, the current density (CD) increases. For example: at 0.270 mass-fraction of anode-water inlet, the average CD is 2062 A/m² while at 0.594 mass-fraction of anode-water, the corresponding value is 7209 A/m². Also the flow patterns for hydrogen and oxygen at the electrode-electrolyte interface were obtained, which helps in the prediction of any reactant starved areas. Experiments were conducted using the single cell PEMFC stack developed by us at The University of Alabama. The model results agree well with the experimental data at temperature and pressure of 350 K and 240 kPa respectively. The present model results can be applied in development of industrial scale fuel cells and optimizing the fuel cell efficiency.