United Airlines and American Airlines are intensifying their rivalry at Chicago O'Hare International Airport, competing over gates, routes and market share at one of the world's busiest hubs, reports the American Journal of Transportation.

United, headquartered in Chicago, has rebuilt faster since the pandemic and plans nearly 650 daily flights to about 200 destinations this summer. American, calling O'Hare its third-largest hub, will lift spring operations above 500 daily flights, adding about 100 peak-day services and extending transatlantic routes to Paris and Dublin.

United said it cancelled only 1 per cent of scheduled flights last year, its lowest rate at O'Hare, and holds a 20 percentage-point lead in local passenger share. Chief executive Scott Kirby questioned whether American's comeback is sustainable, while American CEO Robert Isom insisted Chicago can support two major hub carriers.

Analysts say access to gates and schedules, not fares, now sets the pecking order. O'Hare grew faster than any other major US hub last year in passenger numbers, departures and gate use, according to DePaul University professor Joseph Schwieterman.

United has expanded premium seating, lounges and high-speed Wi-Fi, while American has upgraded its fleet to offer premium seating on every O'Hare departure and deployed Boeing 787-9 aircraft on its Chicago-London route. Loyalty enrolments in Chicago rose 20 per cent in the third quarter of 2025.

United operates about half of all scheduled flights at O'Hare, compared with a third for American. The gap widened after United gained five gates and American lost four in a city reallocation. American has since bought two gates from Spirit Airlines for US$30 million to recover capacity.

Aviation commissioner Michael McMurray said the rivalry reflects Chicago's strength, with an $8.5 billion terminal expansion adding gates over the next decade. Consultant Robert Mann warned American's growth without matching gate access could strain operations, while United may need deeper discounts to defend share. Customers may benefit from more flights and lower fares in the short term.