The Biggest U.S. Airlines, Ranked by Sustainability (2023)

If an American with an average footprint flies from New York to San Francisco roundtrip, those 12 hours in the air would make up 5% of their annual emissions.

But not all flights have the same emissions. The airline you choose could result in a 74% higher or lower footprint. Fuel usage is the most prominent driver of an airline’s emissions. We ranked the biggest U.S. airlines by their fuel usage per passenger mile to determine the most sustainable airlines of 2023.

The Airlines We Ranked

Commons ranked 11 of the biggest airlines in the U.S. by gallons of fuel burned per revenue passenger mile (RPM):

  • Alaska Airlines
  • Allegiant
  • American Airlines
  • Delta
  • Frontier
  • Hawaiian
  • JetBlue Airways
  • Spirit
  • Southwest Airlines
  • Sun Country
  • United Airlines

RPM (revenue passenger miles) measures the number of miles traveled by paying passengers. This differs from APM (available passenger miles) because APM is the total amount of seats available on the plane. 

Our Methodology

We ranked airlines based on their gallons of fuel burned per RPM to determine our sustainability ranking. 

Emissions per revenue passenger mile (RPM)

The gallons of fuel per passenger mile tell us how efficiently the airline is flying based on how many people are on the plane and how much fuel the plane is burning per mile. 

Our fuel/RPM calculation does not account for the efficiency or emissions of more sustainable fuels. Sustainable aviation fuel (SAF) production tripled from 2021 to 2022, but SAF accounted for less than 0.1 % of the total jet fuel used by major U.S. airlines last year. 

As SAF becomes more prevalent, factoring in fuel efficiency will garner a more accurate estimate. With our current calculations, we assume that all jet fuel is the same.

CDP Scoring

The CDP (Carbon Disclosure Project) has become a standard for sustainability disclosure. Big companies and corporations — from Walmart to American Airlines — have disclosed environmental data through CDP’s climate change questionnaire. 

CDP’s scoring is based on the amount and comprehensiveness of the data companies provide. While we didn't account for CDP scoring in our overall ranking, it's important to further contextualize other sustainability efforts and goals.

Why are budget airlines more sustainable?

There are a couple of reasons why budget airlines rank highest on our list. 

First, budget airlines’ gallons-per-RPM are lower because they fit more seats onto their planes. While fuel efficiency decreases slightly with more weight from more passengers, ultimately, fuel-per-passenger is lower when the number of passengers is higher. 

Denser seating charts result in less legroom and less emissions per passenger. The more people in a plane, the lower the emissions per passenger. 

The second reason budget airlines have fuel usage is because they lower the weight per passenger by lowering the amount of luggage and in-flight concessions. By charging for baggage, customers have an incentive to pack lighter, resulting in less weight on the plane. By charging for in-flight concessions, the flight crew doesn’t need to carry as many heavy beverages and food. 

 

On our list, budget airlines average 12.6 gallons of fuel per RPM. While traditional airlines average 16.5. 

1. Frontier 

As of January 2023, Frontier claims to have the youngest fleet in the industry. These newer planes burn less fuel. They also use Pratt & Whitney GTF™ engines which claim to be the most fuel-efficient, lowest carbon-emitting engine for A320neo family aircraft. A20s make up 67% of Frontier’s fleet, but it’s unclear if all of their A20s use this more efficient engine. 

As a secondary fuel efficiency measure, Frontier is reducing weight across its seats through 2028. They’re also removing in-flight entertainment to cut down on weight.

As a budget airline, Frontier also lowers fuel usage by reducing the amount of luggage and in-flight concessions. 

2. Sun Country 

  • CDP score: F (no response) 
  • Fuel per revenue passenger mile: 12.5

There was no information available about Sun Country’s sustainability efforts or goals. As a budget airline, their RPM ranks near the top (read: lowest) because they’re reducing the amount of luggage and in-flight concessions. 

3. Spirit 

Like Frontier and Sun Country, Spirit is a budget airline, which means that its RPM is lower because their planes carry more people, less luggage, and fewer in-flight concessions. 

It’s important to note that Spirit Airlines hasn’t released a sustainability report since 2020, so the data here is older than for all other airlines. 

In 2022, Spirit added more A20neo aircraft to its fleet. These aircraft are reported to be one of the most efficient commercial aircraft available. As of 2023, these make up 71% of Spirit’s fleet, and the airline claims that these planes burn 15-20% less fuel than others in their fleet.

Efforts in 2019 and 2020 to improve flight planning and reduce unnecessary planned fuel resulted in an emissions reduction of over 6,560 tCO2e.

4. Allegiant 

As of October 2023, there is no information available about Allegiant’s sustainability efforts or goals in 2022. Based on their 2021 report, they’ve employed various techniques to reduce fuel usage by using less engine power and reducing drag. 

Allegiant is also a budget airline, so its low RPM can also be attributed to transporting more people in each plane with less luggage and fewer in-flight concessions. 

5. Alaska 

Among non-budget airlines, Alaska Airlines consistently ranks high for its gallons-per-RPM which is about 10% lower than the average among non-budget airlines. 

The International Council on Clean Transportation ranked Alaska Airlines number one in fuel efficiency for five years in a row. The airline purchased more SAF in 2022 than in years prior.

On board, Alaska also incentivizes less waste by requiring passengers to pre-order their meals. By pre-ordering, Alaska only brings on board the meals they need. In 2022, they made a huge stride in reducing plastic use by bringing the first airline to fully transition to paper cups.

6. Southwest Airlines

In their sustainability reporting, Southwest shows that from 2001 to 2022, they reduced their Available Seat Mile emissions by over 10% by introducing newer, more fuel-efficient planes.

Southwest’s SAF goal is to replace 10% of its fuel by 2030. As of 2022, they’re 0.5% toward that goal. Also, by 2030, they plan to reduce carbon emissions intensity by 25%. They’re 1.9% to that goal.

7. JetBlue 

JetBlue ranks the lowest of all the budget airlines for the fuel per paid passenger.

JetBlue reports having a total of 100 A220 aircraft either delivered or ordered as of July 2022. According to their projections, these planes burn up to 35% less fuel per seat and CO2 than older planes, as well as around 50% less NOx emissions than industry standards.

On board, JetBlue has some single-use plastic goals focused on either reduction or recycling, but it’s unclear exactly how much plastic the company avoids vs recycles.

8. Hawaiian Airlines

Hawaiian Airlines has done more cargo shipping to compensate for passenger reductions from the pandemic. When looking at all their flights, carbon intensity increased by 4% from 2021 to 2022. The rate of increase was higher in passenger flights at 5%.

In their goals for the future, Hawaiian cites the increasing usage of sustainable aviation fuel (SAF) as a key way to reduce the emissions of their routes. It’s unclear how much progress toward their goal of replacing 10% of conventional jet fuel with SAF by 2030. 

9. United Air Lines

Like most airlines on the list, United is also investing in SAF as a path forward. Of their accolades, they claim to have the first-of-its-kind SAF-focused investment vehicle: the Sustainable Flight Fund. In 2021, theirs was the first passenger flight to use 100% SAF fuel in one engine. But it's important to note that the SAF industry can't currently meet the demand of commercial airlines.

To reduce their emissions, United has forecasted 30% more fuel efficient flights by 2050 through improved engines, and newer aircrafts in the fleet. United also pledged a net zero goal by 2050 without relying on the use of traditional carbon offsets.

10. Delta Air Lines

In 2022, they improved the fuel efficiency of their fleet by 4.5% with the addition of 69 newer, more fuel-efficient planes to their fleet. Fleet renewal seems to be their biggest sustainability focus for reducing emissions intensity. They also procured 329% more SAF (sustainable aviation fuel) in 2022 than in 2021.

As of 2022, Delta’s 2050 goals are still under review by SBTi. They have contracts to obtain more sustainable aviation fuel SAF, but it’s unclear if they’ve started using SAFs. 

To reduce plastic use, Delta reportedly replaced some of their cutlery with reusable or biodegradable materials and replaced some plastic wine bottles with cans. With these efforts in addition to replacing bedding with materials made from recycled plastic bottles, Delta projects that they’ll reduce their on-board single-use plastic consumption by about 4.9 million pounds per year.

11. American Airlines

Among American Airlines’ goals are flying newer, more fuel-efficient aircraft, sourcing more renewable energy, and reducing overall GHG emission intensity. In 2022, over 21% of their ASMs (available seat miles, aka total seats on the plane) were flown on latest-generation aircrafts. AA’s goal is to reach 30% by 2025.   

They’ve made progress in fuel efficiency by flying more young planes and purchasing more renewable energy, but they’re falling short of their carbon intensity goal. Their goal is to reduce carbon intensity by 45%, but they’ve only reduced it by 2.7% as of 2022.

American Airlines stands out with the highest CDP score of the passenger airlines.

According to American Airlines, their 2035 targets comply with SBTi’s (Science Based Target) aviation criteria. According to SBTi, the criteria “allows aviation companies to meet the minimum ambition levels required by the criteria and provides a short-term, accessible option for them to set science-based net-zero targets.”

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