The International Energy Agency (IEA) expects that by 2040 reductions in energy intensity will contribute 42 per cent of the reduction in greenhouse gas emissions relative to business as usual required to achieve the goal of limiting climate change to a 2°C increase in temperature. The majority of the improvement in energy intensity is seen as coming from improvements in the energy efficiency of energy services. On the other hand, the mechanisms enabling the geographical spread of such energy-saving technological improvements have not been sufficiently investigated. The passenger airline industry is perhaps unique in the availability of global data on installed equipment at the individual machine and firm level together with comprehensive information on model energy efficiency. In this paper, we investigate the factors that affect the selection of fleet fuel efficiency by airlines across countries.