Hainan Airlines and All Nippon Airways (ANA) ranked first in overall fuel efficiency, both with an average fuel efficiency of 36 passenger-kilometers per liter of fuel (pax-km/L), according to a recently released study by the International Council on Clean Transportation (ICCT) on the 2016 fuel efficiency statistics for transpacific airlines. Qantas Airways ranked as the least fuel-efficient of the 20 airlines operating nonstop flights between the mainland U.S. and East Asia/Oceania, burning an average of 64 percent more fuel per passenger-kilometer than Hainan and ANA. According to the report, freight share was the most important driver of fuel efficiency overall, explaining almost half of the variation in airline fuel efficiency across carriers, followed by seating density.

The findings, based on Bureau of Transportation Statistics data compiled by Texas-based airline consultancy Airline Data Inc. (formerly Data Base Products) showed that Air New Zealand, EVA Air, and China Airlines (the latter two tied for fourth place) rounded out the top five fuel-efficient transpacific airlines. In its white paper, ICCT stated that there is an inverse relationship between aircraft size and fuel efficiency on transpacific operations. As aircraft weight, or maximum takeoff mass (MTOM), increases, fuel efficiency declines. It determined that this is predominantly because aircraft with four engines are generally less fuel-efficient than those with two.

ICCT is an independent nonprofit organization founded to provide technical and scientific analysis to environmental regulators. It has applied Airline Data’s analysis in the past, such as in its evaluation of the fuel efficiency of domestic U.S. carriers.

“Accurate, quality data empowers people and organizations throughout the industry to make informed business decisions,” said Jeff Pelletier, the company’s managing director. “Our data has been a trusted source of information for more than 30 years and we’re proud to be an ongoing part of ICCT’s fuel efficiency research program.”