A metal hydride based hydrogen compressor using MmNi(4.6)Al(0.4) is tested at both constant and variable delivery pressures. The effects of operating parameters such as supply pressure and heat source temperature on the compressor performance are investigated. The compressor yields a maximum isentropic efficiency of 7.3% at 95 degrees C heat source temperature at variable delivery pressure operation mode, and 14.2% at 85 degrees C heat source temperature at constant delivery pressure operation mode. At both the operation modes, the volumetric efficiency of the compressor is found to decrease at high heat source temperatures. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.