In this paper, an exergoeconomic analysis of a 12900 kW PEM electrolyser developed by WE-NET at various operating temperatures and pressures is conducted. The analysis is performed at electrolyser's operating temperatures (T/T-0) and pressures (P/P-0) ranging from 1 to 1.4 and 1 to 10, respectively. A 40% improvement in the exergy cost of hydrogen could be achieved by operating the PEM electrolyser at a low temperature. However, a 2% decrease in the exergy cost could be achieved if the operating pressure is increased from 1 to 10 atm. Furthermore, a lower annual capital cost, O&M cost, electricity cost and higher year life could contribute greatly in reducing the exergy cost of hydrogen. Copyright © 2005 John Wiley & Sons, Ltd.