High performance and efficiency are often reported in single-cell polymer electrolyte membrane (PEM) fuel cell (FC) experiments. This however, can reduce substantially when moving from single-cell experiments to multiple cells. Fuel cell performance is degraded for many reasons when adding cells, but; possibly the most important, is contact resistance between the bipolar plate and gas diffusion layer (GDL). Contact resistance is in direct relation to the clamping configuration and clamping pressure applied to a FC stack. Simulation of a single cell and 16-cell PC was performed at various clamping pressures resulting in detailed 3D plots of stress and deformation. The stress on the GDL, for any value of clamping pressure simulated in this study, is around 1.5 MPa for the 16-cell stack and around 4 MPa in single cell simulations. Experimental testing of clamping pressure effects was performed on a 16-cell stack by placing a thin pressure-sensitive film between GDL and bipolar plate. Clamping pressure was applied using various loads, durations, and two types of GDLs. The results from experimental testing show that pressure on the GDL is in the range of 0-2.5 MPa. When using rectangular cells, experimental results show nearly zero pressure in the center of each cell and the center cells of the stack, regardless of clamping method. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.