LONDON (July 2, 2025) – Wizz Air is the world’s most emissions-efficient airline in new rankings released today by Cirium. The Cirium Flight Emissions Review ranks the top 20 airlines globally, through a consistent benchmark for flight emissions. 

Wizz Air, the Hungary-based ultra-low cost airline emits an industry low of 53.9 grams of CO₂ per Available Seat Kilometer (ASK), followed by Frontier Airlines (54.4 grams) and Pegasus (57.1 grams) according to the report.  

The rankings provide the aviation industry with verified, comparable data on an equal playing field as the sector advances toward Net Zero by 2050 commitments. The rankings performance use Cirium’s EmeraldSky platform, which achieved ISAE 3000 Reasonable Assurance from PricewaterhouseCoopers (PwC) and official accreditation from the Rocky Mountain Institute (RMI). 

Wizz, Frontier, and Pegasus Top 3; The Top 20 Major Airlines Ranked by CO2 Emissions/ASK

The top 20 airlines globally are presented below. 

Of note are the performance of Indigo, top in Asia, Volaris, top in Latin America and the Caribbean, and Jetstar, for its performance in Australia.  

The CO2 Emissions of Largest Airlines in the World 

Cirium’s reporting also ranked the 10 largest airlines in the world by ASK. At the head of the table is Ryanair, followed by Southwest Airlines and Delta Air Lines. Each of the U.S. carriers earned spots on the table, while Turkish Airlines, Qatar Airlines and Emirates rounded out a group of primarily long-haul operators.  

Enabling Fair Comparison Across the Industry 

“For the first time, airlines can compare their emissions performance using a consistent, verified methodology,” said Jeremy Bowen, CEO at Cirium. “EmeraldSky provides the industry-standard benchmark that enables fair comparison and meaningful progress tracking.” 

The comprehensive Review analyzed global operations using dual-accredited methodology, with the full report containing extensive findings across: 

• Global Category Rankings showing the top 20 Major airlines and the Worlds 10 largest airlines by CO₂ per ASK

• Regional Performance breakdowns showing which airlines excel on intra-region and inter-region routes 

• Route-Level Improvements identifying specific airport pairs with the greatest efficiency gains 

• Operational Insights revealing how fleet composition, load factors, and route optimization drive performance differences 

The Review provides comprehensive operational insights that support industry-wide efficiency improvements, offering actionable intelligence for aviation stakeholders committed to sustainability progress.

Setting New Industry Transparency Standards 

EmeraldSky’s methodology achieved the highest level of assurance under the International Standard on Assurance Engagements through rigorous independent review. The Rocky Mountain Institute’s accreditation under the Pegasus Guidelines validates the approach for climate-aligned aviation financing, enabling banks and investors to make informed decisions based on verified emissions data. 

This standardized approach addresses aviation’s fragmented sustainability reporting, where inconsistent methodologies have made meaningful comparisons impossible. The verified benchmark enables airlines to assess their operational efficiency accurately, investors to evaluate performance reliably, and corporations to report Scope 3 emissions with confidence. 

Quarterly Updates Drive Accountability 

The Flight Emissions Review will be updated quarterly, tracking performance changes and operational improvements across the industry. With hundreds of data points and detailed analysis across multiple categories, the report provides the most comprehensive view of aviation emissions performance available. 

Access the Complete Rankings and Analysis 

The full Flight Emissions Review, including detailed carrier rankings, regional breakdowns, route-specific analysis, and operational insights, is available for download at www.cirium.com/flight-emissions-review. 

About Cirium 
Cirium^® is the world’s most trusted source of aviation analytics. The company delivers powerful data and cutting-edge analytics to empower a wide spectrum of industry players. It equips airlines, airports, travel enterprises, aircraft manufacturers, and financial entities with the clarity and intelligence they need to optimize their operations, make informed decisions, and accelerate revenue growth. 

Cirium^® is part of LexisNexis^® Risk Solutions, a RELX business, which provides information-based analytics and decision tools for professional and business customers.  The shares of RELX PLC are traded on the London, Amsterdam and New York Stock Exchanges using the following ticker symbols: London: REL; Amsterdam: REN; New York: RELX. 

Download the complete Flight Emissions Review with full rankings, regional analysis, and operational insights at www.cirium.com/flight-emissions-review 

For Cirium media inquiries please contact media@cirium.com