Commercial sized (16 x 16 cm(2) active surface area) proton exchange membrane (PEM) fuel cells with serpentine flow chambers are fabricated. The GORE-TEX (R) PRIMEA 5621 was used with a 35-mu m-thick PEM with an anode catalyst layer with 0.45 mg cm(-2) Pt and cathode catalyst layer with 0.6 mg cm(-2) Pt and Ru or GORE-TEX (R) PRIMEA 57 was used with an 18-mu m-thick PEM with an anode catalyst layer at 0.2 mg cm(-2) Pt and cathode catalyst layer at 0.4 mg cm(-2) of Pt and Ru. At the specified cell and humidification temperatures, the thin PRIMEA 57 membrane yields better cell performance than the thick PRIMEA 5621 membrane, since hydration of the former is more easily maintained with the limited amount of produced water. Sufficient humidification at both the cathode and anode sides is essential to achieve high cell performance with a thick membrane, like the PRIMEA 5621. The optimal cell temperature to produce the best cell performance with PRIMEA 5621 is close to the humidification temperature. For PRIMEA 57, however, optimal cell temperature exceeds the humidification temperature. (C) 2010 Elsevier Ltd. All rights reserved.