The report said Qantas recorded poor fuel efficiency because it used older, fuel-intensive aircraft, carried a low amount of freight (therefore making it less efficient) and also had relatively low numbers of passengers on each plane.
In a statement Tuesday, Qantas Head of Fuel and Environment Alan Milne said the airline ranked poorly because "we use larger aircraft, fly very long distances and have premium cabins that naturally have fewer people on board."
Milne added that the airline's Sydney to Dallas route, as one of the longest in the world, had a magnifying effect on emissions because at take-off there was so much fuel to carry
Qantas was the only airline in the list to have the Airbus A380 as its most prevalent aircraft on transpacific routes. The carrier said it is committed to lowering emissions and would soon be switching old 747's for Boeing's more fuel-efficient Dreamliner range.