Hydrogen could provide a pathway to long-term sustainable aviation provided its use does not excessively penalise aircraft performance and energy efficiency. To assess the implications of hydrogen use in aviation a study on the energy efficiency of kerosene- and hydrogen-fuelled aircraft is presented. The investigation shows that the use of hydrogen for long-range operation can lead to an increase in energy efficiency of up to 12% compared to kerosene. For short-to-medium-range aircraft, on the other hand, the adoption of hydrogen leads to an increase in the mission energy requirement of 5-18%. Storing hydrogen on top of the cabin instead of in tanks located in front and aft of it has a considerable impact on the energy efficiency. The increased weight of the top tanks leads to an increase in energy use of 6 and 19% for the selected notional short-respectively medium-range aircraft. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.