These Are the Most Affordable (and Most Expensive) U.S. Airlines

Frontier Airlines is the cheapest carrier in the United States, despite its history of upselling customers for things like bags and seat selection.

The ranking is courtesy of a new study from airline compensation company AirAdvisor shared with Travel + Leisure, which looked at total passenger revenue per seat mile for the top 10 airlines in the U.S. When it comes to Frontier, the airline was more than $0.01 per mile cheaper than the next cheapest airline, fellow low-cost carrier Spirit Airlines.

“Frontier Airlines is often referred to as an ultra-low-cost carrier, and this certainly rings true based on our research,” AirAdvisor wrote in the study. “US airlines don’t get any cheaper than this as a whole.”

The ranking comes as both Frontier and Spirit recently eliminated most change and cancellation fees and Spirit made it easier to use travel vouchers for longer.  

Next on the list was Hawaiian Airlines, which came in as the third cheapest airline and the cheapest non-ultra-low cost carrier. In fact, AirAdvisor found Hawaiian Airlines was “by far the best combination of reliability and price of any airline we reviewed.”

Low-cost airline Allegiant Air and JetBlue rounded out the top five, but AirAdvisor noted Allegiant’s revenue per seat mile was $0.03 more than Frontier’s.

On the other end of the spectrum was Delta Air Lines, which came in as the most expensive airline per mile, but also one of the most reliable. That said, there are still ways to save.

“Delta offers flights all over the world, so there is a place for them on the itinerary of even the most budget-conscious traveler,” AirAdvisor wrote in the report. “Their website has a section for current flight deals, and you can subscribe to their newsletter to be informed whenever new sales are starting.”

Delta was followed by Southwest Airlines, which came in as the second most expensive on the list. That was due, in part, to the airline’s optional upgraded fare categories that come with perks like seat selection.

To form the list, AirAdvisor said it averaged the revenue per available seat mile for each airline in 2022 and 2023. The company specializes in helping travelers collect compensation from airlines when they are owed and collects a commission when the airline pays.

Beyond booking the cheapest airlines, travelers can save by buying tickets with specific airlines on certain days, being flexible, and setting price alerts.