The hyperstoichiometric ZrMnFe x system with x = 1.2-1.4 has been studied as a hydrogen storage material. The stoichiometric excess iron exhibits a profound promoting effect on the decomposition pressure of the hydride. The hydrogen capacity was observed to be very sensitive to the hyperstoichiometric iron content. The host metal underwent a 13% lattice expansion with no structural transformation during hydrogenation. The configurational entropy of hydrogen in the hydride phase is similar to that of deuterium in the ZrMn 2 deuteride, suggesting a similar site occupancy situation. The extreme rapidity of hydrogen sorption is attributed to a 3-dimensional network for hydrogen diffusion existing in the hydride lattice.