Proton exchange membrane fuel cell is a promising clean energy conversion device. Proton exchange membrane fuel cell power system has great potential in the automotive applications. A fuel cell stack and an air compressor are two important components in a fuel cell power system and it is meaningful to study their properties for better system performance. The aim of this study is to enhance the performance of a 20 kW vehicular proton exchange membrane fuel cell power system incorporating a fuel cell stack and an air compressor, through the cathode operating pressure optimization. The fuel cell stack is investigated numerically and the air compressor characteristics are obtained experimentally. The fuel cell stack and the air compressor are matched properly, and then the operating pressure optimization for the power system is carried out. The results of this study show that the fuel cell stack power generation is increased with the system operating pressure. The compressor power consumption is also increased with the system operating pressure, but it can be reduced by using a two-speed compressor operation mode. The optimum system operating pressure is found to be 1.2 atm. The optimum system operating pressure is influenced by the compressor efficiency and is increased with the compressor efficiency. (C) 2017 Elsevier Ltd. All rights reserved.