Hydrogen is potentially the fuel of the future, with the transition to a hydrogen economy driven by the concerns about the climate change and the depletion of fossil fuel resources. Hydrogen is better than almost all other fuels when the fuels are evaluated on the basis of several metrics, including safety and versatility of use. Hydrogen is also presumed to have a superior motivity factor, a performance measure arising out of a combination of acceleration and drag forces. The motivity factor is quantified on the basis of the gravimetric and volumetric energy densities of a fuel. The present paper offers a refinement of the motivity factor which incorporates the effects of the mass of the storage matrix in these energy densities. It is shown that other fuels may have higher motivity factors than hydrogen when quantified on the basis of these refinements. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.