Scoot, the Singapore low-cost carrier, topped the list of the world’s most emissions-efficient airlines in Cirium’s 2025 EmeraldSky Annual Review. The carrier is the first Southeast Asian airline to lead in global airline emissions efficiency rankings, claiming the top spot from 2024’s frontrunner, Wizz Air, which placed second this year.

Now in its second year, Cirium’s EmeraldSky rankings are based on CO₂ per ASK across the world’s 100 largest airlines, using flight-level operational data. Airlines are grouped into Gold, Silver and Bronze tiers based on global performance, covering the top 15 airlines as well as key regional and route performers. The methodology is independently assured by PwC under ISAE 3000 standards.

In this year’s rankings, TUI Airways, Air Europa and Frontier Airlines rounded out the top five carriers, all earning Gold status. In addition to Frontier, the other North American carriers ranking in the top 15 were Spirit Airlines and WestJet.

The results of the Cirium analysis shows that airlines, especially low-cost carriers operating younger fleets with higher seat density, continue to lead the industry in emissions efficiency. For example, this year’s leader, Scoot, has one of the newest fleets on the list operating on longer average sectors with an average seat density of 242 seats per aircraft.

Meanwhile, long-haul airlines are upping their emissions efficiencies primarily by fleet renewal, removing from service older, less-fuel-efficient aircraft. Among global airlines, Qatar Airways, Ryanair, and Turkish Airlines were named the top three most efficient ranked by available seat kilometers. Korean Air recorded the largest long-haul route improvements globally, driven by the transition to next-generation aircraft on key transpacific routes.

“Airline emissions performance comes down to decisions airlines can control – fleet choices, seat configuration and how aircraft are deployed on routes,” said Jeremy Bowen, CEO of Cirium. “The airlines at the top of these rankings have got those fundamentals right, and it shows. Better emissions efficiency and lower fuel bills go hand in hand.”