Each year, several organisations attempt to provide rankings of the efficiency of airlines. Please find below a commentary on these studies.
We do not believe these blunt fuel efficiency rankings provide an accurate reflection of the sustainability of individual airline operators and in fact could lead to consumers being misled into making incorrect choices. In particular, the annual rankings by the International Council for Clean Transportation (ICCT) and Atmosfair tend to often provide conflicting reports and are not based on accurate data from the airline operators themselves. They are likely modelled in good faith, but their results are questionable and should not be seen as the standard for decisions by travellers or corporate travel agencies.