Potential of a novel hydrogen storage vessel, "hybrid hydrogen storage vessel", combining an aluminum-carbon fiber reinforced plastic (Al-CFRP) composite vessel and hydrogen storage alloy, is reported through calculation of the weight and volume of the hydrogen storage system for 5 kg of hydrogen. Evaluation of this system showed that the concept of the hybrid hydrogen storage vessel allowed us to realize a hydrogen storage system advantageous in both gravimetric and volumetric hydrogen density compared with conventional hydrogen storage techniques. The hybrid vessel requires a hydrogen storage alloy with a higher volumetric hydrogen density as well as a higher gravimetric density, and with a higher equilibrium hydrogen pressure than the hydrogen storage alloys which have been used for conventional hydrogen storage vessels. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.