This paper describes the development of a unique single cell proton exchange membrane (PEM) test fixture to independently investigate the effects of gas sealing and assembly pressure. The test fixture is shown to provide useful insights into the effects of pressure on contact resistance. Two versions of gas diffusion layers (GDL) were tested to demonstrate that contact pressure significantly affects cell performance. In general, performance tends to increase with clamping force until a plateau is reached, after which performance drops rapidly. The rapid drop at high GDL pressure is due to puncture of the membrane or GDL mechanical failure. The performance improvements with pressure may be due to reductions in electrical or ionic resistance.