How do airlines rank in emissions efficiency? Cirium releases annual review

Singapore-based Scoot has been ranked the world’s most emissions-efficient airline in Cirium’s 2025 EmeraldSky Annual Review, overtaking last year’s leader, Wizz Air.

Meanwhile, Qatar Airways, Ryanair, and Turkish Airlines were identified as the top three most efficient global carriers based on available seat kilometres (ASK).

The rankings, produced by Cirium, evaluate CO₂ emissions per available ASK across the 100 largest airlines worldwide.

The methodology is independently verified by PwC under the ISAE 3000 standard.

Airlines are then classified into Gold, Silver, and Bronze tiers according to their overall performance, including the top 15 global airlines along with leading regional and route-specific 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, in a press release. “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 continues to be one of the strongest performers, supported by a relatively young fleet averaging under five years, a pattern also seen at airlines such as Frontier Airlines and IndiGo.

In contrast, long-haul carriers are narrowing the emissions gap mainly through fleet renewal programmes, phasing out older, less fuel-efficient aircraft.

Operators like Virgin Atlantic show that modern widebody jets combined with higher-density cabin layouts can achieve strong emissions efficiency even on long-haul routes.

Across all regions, airlines with newer aircraft and greater seat density consistently rank at the top within their respective markets, though comparisons vary depending on regional operating conditions and metrics.

In the Intra-North America category, WestJet ranked third behind Spirit and Frontier. Whereas in Cirium’s transatlantic category, Air Canada ranked second, in between Virgin Atlantic (first) and Aer Lingus (third).

The review also shows whether airlines are growing capacity faster than emissions.

One table 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," stated 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."

You can view the full report here.

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