The airline industry's biggest profit engine no longer ends with summer.

Delta Air LinesDAL

and United AirlinesUAL

shares each hit record highs recently. American AirlinesAAL

touched an 18-month high. The US Global Jets ETFJETS

, a broad proxy for the sector, gained 13% in June alone and hit its own record.

What's driving the season shift

The structural story here is about the shoulder season. That's the travel industry term for the period between peak and off-peak. Airlines are actively expanding into that window, and it's becoming a real revenue driver.

Delta's VP of international network planning said the airline is now scheduling maintenance in the summer to preserve planes for fall. That's a full reversal of the old playbook, where summer was untouchable, and maintenance happened in the winter quiet.

United's nonstop flight from Newark to Palermo, Sicily, now runs through Dec. 16, well past the traditional September cutoff. Delta extended its JFK-to-Catania route through Jan. 3 and plans to restart it March 8, 2027. Americans call October a peak month now, not just a filler period between summer and the holidays.

Alaska AirlinesALK

, which launched its first transatlantic routes this year, is also banking on year-round demand flexibility.

Why travelers are actually showing up

Record heat waves across Europe this summer pushed travelers toward cooler, cheaper months. European cities have also faced overcrowding concerns during peak periods, giving travelers more reason to explore alternatives.

Beyond weather, work flexibility matters. Alaska Air's CFO noted that parents are increasingly willing to pull kids from school for off-peak trips. Baby Boomers with time and savings are also filling seats outside traditional vacation windows.

Demand data backs this up. United expects more than 53M passengers from June through August. American projected ~75M customers across ~750K flights for its centennial summer. Southwest CEO Bob Jordan said there's been no demand drop-off despite repeated fare increases.

The fuel tailwind supercharging margins

Jet fuel is the industry's second-largest cost after labor, accounting for 25% to 30% of total operating expenses. In early April, fuel spiked to nearly $4.88 per gallon after the Strait of Hormuz closed during the US-Iran conflict. It's now back around $2.91 per gallon following a cease-fire agreement.

That swing is enormous for profitability. Airlines had already cut less profitable routes and raised fees to absorb the spike. With fuel retreating while fares hold, margins expand quickly.

Average ticket prices rose more than 18% year over year in May, according to Bank of America analysts citing Airline Reporting data.

Economy fares rose more than 20%, outpacing premium fares for the third straight month. Domestic routes saw the sharpest increases, with some hot routes surging 35% versus a 15% rise for international fares.

Airlines aren't rushing to hand savings back to customers either. United's CEO said in an April earnings call he expects the carrier to retain at least 20% of price increases even if conditions normalize.

How to think about exposure here

Morgan Stanley recently said airline stocks are set to hit or beat the high end of second-quarter guidance. Delta kicks off earnings season on July 10, with American and United reporting the following week.

The premium cabin buildout adds another layer. United expanded business and premium economy seats by 40% between 2019 and 2025.

American grew premium seating 16% over the same period versus just 5% for economy. Business-class fares on transatlantic routes can hit $10K round-trip, vs. under $5K on domestic routes.

The risk that remains is real. IATA projects fuel costs will take a $100B bite out of industry profits this year.

The Iran cease-fire is only a 60-day framework, meaning oil prices could reverse. Capacity constraints from BoeingBA

and Airbus delivery backlogs limit upside flexibility.

But the structural shift in travel patterns, like longer seasons, premium demand, and a leaner competitive landscape after Spirit Airlines' collapse, gives the major carriers durable pricing power that didn't exist three years ago.