United Airlines’ 737-9 Fleet Set to Surpass 737-900ER

United Airlines is rapidly expanding its Boeing 737-9 Max fleet, taking delivery of five jets in just seven days—nearly one per workday. The surge underscores both United’s aggressive growth strategy and improving production flows at Boeing.

According to chaviation.com, United currently operates 136 Boeing 737-900ERs, the predecessor to the 737-9. With 111 MAX 9s now in service and another 114 on order, the airline is on track to see its 737-9 fleet soon surpass the size of its 737-900ER fleet.

United’s reliance on the 737 family traces back to its merger with Continental Airlines, which originally brought most of the 737NG fleet. Before the merger, United focused more on Airbus A319s, A320s, and Boeing 757-200s for short-haul routes. Afterward, the carrier expanded its Boeing orders and placed a massive commitment to the 737 MAX program.

While the NG fleet remains steady, United is accelerating retirements of its oldest Airbus A320-200s. This has tipped the balance of its narrowbody operations, with more than half of United’s entire fleet now composed of 737s. Most new deliveries—737-9s and incoming Airbus A321neos—are earmarked for growth rather than pure replacement.

Fleet upgauging is central to United’s strategy: larger jets are being deployed on existing routes, freeing up smaller aircraft to launch new ones. The 737-9, seating around 179 passengers, effectively bridges the gap between the 737-8 (166 seats) and Airbus A321neo (200 seats). While the A321neo offers lower per-seat fuel burn, the 737-9 remains competitive with overall lower fuel consumption and flexibility across United’s short-haul network.

Originally, United had planned for the 737-10 to anchor its domestic growth, converting 100 MAX 9 orders and adding more. However, with certification delays pushing entry into service to 2026, CEO Scott Kirby announced in 2024 that the airline removed the MAX 10 from its near-term planning. Many orders have since reverted to the 737-9, which now stands at 167 firm orders. Ultimately, United is expected to operate over 200 MAX 9s, making it the most common 737 variant in its fleet.

United Airlines Narrowbody Fleet, as of August 2025:

Airbus A319-100 In service 80 Retiring 21 older aircraft in 2025.
Airbus A320-200 In service 74
Airbus A321neo In service 45 Orders 157 Deliveries until 2032.
Airbus A321XLR Orders 50 Deliveries start in January 2026, replacing Boeing 757-200.
Boeing 737-700 In service 40
Boeing 737-800 In service 139
Boeing 737-900 In service 12
Boeing 737-900ER In service 135
Boeing 737-8 In service 123
Boeing 737-9 In service 107 Orders 117 Largest operator.
Boeing 737-10 Orders 167 Production halted amid certification uncertainties; orders may be converted to 737-8 or 9.
Boeing 757-200 In service 40 To be replaced by Airbus A321XLR.
Boeing 757-300 In service 21 Largest operator.

Combined, United currently operates 148 737-900/900ER variants and a growing fleet of 737-9s. With more than 50% of its total fleet made up of Boeing 737s, United continues to shift toward 737 MAX aircraft while phasing out older Airbus narrowbodies.

United’s rapid 737-9 expansion highlights both the challenges of relying on delayed programs and the adaptability of its fleet strategy. For now, the MAX 9 has become the workhorse of United’s domestic and short-haul international network, ensuring steady growth while the industry awaits the arrival of the 737-10.

Sources: AirGuide Business airguide.info, bing.com, CHAviation.com