The reason is simple: a week after Spirit Aviation Holdings Inc. ceased operations, Frontier is executing on a strategy its CEO said has been in the works for months, pouncing on market share left on the table after Spirit went out of business.

The airline is adding capacity into airports such as Orlando, Las Vegas and Dallas-Fort Worth, where Spirit had a large presence, according to a Bloomberg analysis of Cirium flight data. Frontier has added 3 million seats in the last week to its scheduled flying between June and September, the analysis shows. 

“Spirit’s exit meaningfully alters the supply landscape,” Frontier Chief Executive Officer James Dempsey said on an earnings call last week. “We positioned ourselves over the last six to nine months on launching routes that we thought would be opportunities that come as they reduce their capacity and with the possibility that they would cease operations,” Dempsey said. 

The strategy is to win market share and achieve economies of scale, but it’s also not without risk. US airlines spent 56% more on fuel in March from the month before, and any missteps are instantly amplified.

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Frontier’s taking a gamble on the fact that the bottom end of the aviation market is underserved and those customers will still want to fly, but don’t have many options available to them, according to Brandon Parsons, an economist at Pepperdine University’s Graziadio Business School. 

“Frontier operates in a market that’s highly price sensitive, and with Spirit’s exit, that market is underserved at the moment,” Parsons said. “They’re taking a long-term view, although it’s not without risk as you still need to get through the short term to survive long term.”

Jet fuel can account for as much as a third of airlines’ costs, and the largest US carriers including United Airlines Holdings Inc., Delta Air Lines Inc. and American Airlines Group Inc., have all said they will hold back capacity in order to protect margins.

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United CEO Scott Kirby has been a vocal critic of ultra-low-cost carriers and has previously said that Spirit’s business model didn’t work in the US. 

“I think airlines want to return their cost of capital and particularly here in the United States, most don’t,” Kirby said on an analyst call last month. “And that is unsustainable in the long run. So something had to change. It’s unfortunate it had to be an oil crisis, but here we are.”

United has said it is reducing planned growth by about 5%, and now expects capacity — or available seat miles — in the second half of 2026 to be flat to up about 2% from a year earlier.

American Airlines has said it will decide on capacity reductions after monitoring demand. In Europe, Deutsche Lufthansa AG, Air France-KLM and British Airways’ parent IAG SA have all announced plans to pare back capacity growth. 

Shares in Frontier are up about 12% for the year through Friday’s close, while the Bloomberg World Airlines index is down nearly 8%.  

Frontier is not the only carrier that increased capacity in the last week. JetBlue Airways Corp. also added 37,633 seats, Cirium data shows. 

Spirit Airlines ceased operations on May 2 after failing to secure emergency funding. The collapse was preceded by unsuccessful negotiations with the US government about a bailout, two bankruptcy filings and a scuttled merger with JetBlue. 

Dania Beach, Florida-based Spirit, which traces its roots back to the early 1980s, also explored a merger with Frontier in 2025, but those discussions ended without a deal. At the time of its closure, Spirit had a fleet of 96 Airbus A320 and A321 jets in service and another 76 in storage, according to Cirium data. 

Frontier operates an all-Airbus fleet with 183 jets. The airline has previously announced that it will return 24 leased jets and defer the deliveries of 69 new planes from Airbus. 

“We have more route overlap with Spirit than any other US carrier, uniquely positioning us to recapture the demand they left behind,” Frontier’s Chief Commercial Officer Robert Schroeter said on the earnings call. 

Schroeter expects the exit of Spirit to drive up revenue per seat mile by 3% to 5%.

“We’ll continue to be nimble and tightly manage capacity based on fuel and demand trends and accordingly we are reserving updated long-term capacity guidance at this time,” he said.