Many researchers have experimentally studied small (∼10–50 cm2), single cell PEMFC systems to understand the behavior and electrochemistry of PEMFC. Also, three-dimensional electrochemical models have been used to predict the distributions of current, temperature, and species mole fractions as a function of the operating conditions and geometry of small cells and these predictions have been compared with experimental data. However, the commercial viability of PEMFC systems depends on understanding the mass transport and electrochemistry of large-scale electrodes with reacting area on the order of 200–600 cm2 and numerical investigation of PEMFCs of this size have been effectively impossible without the recent advances in parallel computation and processor speed. This paper applies a parallelized three-dimensional computational fluid dynamics (CFD) model to a 480 cm2 PEMFC flow-field selected from US patent literature to demonstrate that analysis of large-scale cells is possible. The distributions of pressure, temperature, and electrochemical variables for stationary and automotive operating conditions are examined. Using parallel computing techniques, the computational time is shown to be significantly reduced by increasing the number of processors while maintaining less than 1% error in mass balance.