Cirium reveals 2025 global airline emissions rankings

Above: Cirium’s 2025 EmeraldSky Annual Review (view the full report here).
Courtesy Cirium

Qatar Airways, Ryanair, and Turkish Airlines were each recognised as the top three most efficient global airlines, ranked by available seat kilometres (ASK).  

Cirium’s ranking is based on CO₂ per available ASK across the world’s 100 largest airlines. The methodology is independently assured by PwC to ISAE 3000. It groups airlines into Gold, Silver and Bronze tiers based on global performance, which covers the top 15 airlines as well as key regional and route performers. 

“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.”

Scoot is the first Southeast Asian carrier to lead in global airline emissions efficiency rankings. Its average seat density of 242 seats per aircraft, operating on longer average sectors, placed it in the lead position this year. The results reinforce a consistent pattern across the industry. Airlines operating younger fleets with higher seat density continue to outperform their peers on emissions efficiency, with low-cost carriers dominating the top of the rankings. Wizz Air placed second (after placing first in 2024), followed by TUI Airways, Air Europa and Frontier Airlines, with all five carriers ranking in the top five globally and earning Gold status. Each has young fleets of aircraft compared to their peers.



Wizz Air remains among the strongest performers with a fleet averaging under five years, similar to other performers such as Frontier Airlines and IndiGo.

Long-haul operators, in contrast, are closing the gap primarily through fleet renewal, by removing from service older, less-fuel-efficient aircraft. Airlines such as Virgin Atlantic demonstrate that newer widebody aircraft and higher-capacity configurations can deliver competitive emissions performance even on long-distance routes.

Top Airlines by ASK
The table below reflects the top three most efficient global airlines, ranked by available seat kilometres (ASK). The top 10 global airlines as ranked by ASK, are listed in the full report.  

 
Regional and Key Intra Regional Rankings
The table below reflects regional rankings, as well as for well-trafficked corridors, the Transatlantic and Transpacific. Across every region, airlines with younger fleets and higher seat density continue to lead within their markets. Results in each region carry their own story as metrics of comparison change. 

 
Airlines Closing the Gap: Capacity Growth Without Emissions Growth
Cirium’s 2025 review shows whether airlines are growing capacity faster than emissions. The table below ranks individual routes by the largest year-on-year reductions in CO2 per ASK and identifies the specific aircraft transition that drove each result. To qualify, a route must have operated at least 300 round trips in the year.

The metric highlights carriers making measurable progress, not just those already operating efficient fleets. Korean Air recorded the largest long-haul route improvements globally, driven by the transition to next-generation aircraft on key transpacific routes. 

 
"The route-level data tells a clear story," said Bowen. "When airlines swap older widebodies for next-generation aircraft, emissions per seat kilometre can fall by as much as 27 percent on that route within a year. This isn’t theoretical — we’re measuring it on real routes with real operational data."

Now in its second year, Cirium’s EmeraldSky Annual Review evaluates airline emissions intensity using CO₂ per available seat kilometre (ASK), based on analysis of the world’s 100 largest scheduled passenger airlines.

The 2025 edition also tracks year-on-year progress, measuring whether airlines are increasing capacity faster than emissions. The methodology uses flight-level operational data and is independently assured under ISAE 3000 by PwC. EmeraldSky is also accredited by the Rocky Mountain Institute as a qualified flight emissions data provider under the Pegasus Guidelines, the first climate-aligned finance framework for aviation.