In comparing different options for producing, distributing and storing hydrogen, it is important to use a consistent set of definitions and to clearly identify assumptions. It is equally important to consider the complete fuel cycle and account for losses, inefficiencies and energy consumption in upstream processes that recover and convert energy feedstock to process fuel. The purpose of this paper is to propose a rational definition of well-to-tank efficiency in terms of the specific energies for hydrogen production, distribution and storage steps. The paper also shows how the specific energies can be consistently calculated by combining information from different processes that comprise the production, distribution and storage steps. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.