Many researchers have stressed the apparently great potential for improvements in energy efficiency to dramatically decrease total energy use, but despite steady progress in the technical efficiency gains, global primary energy use continues to rise. For transport, we show how the concept of energy efficiency has been progressively expanded over time, as our ideas on what constitutes transport output useful to individuals has evolved. Even the energy inputs regarded as necessary for transport have undergone revision, because of the need to compare different modes. Finally we discuss the relevance of the changes in our notions of transport efficiency for energy efficiency in general. (C) 2012 Elsevier Ltd. All rights reserved.