United Airlines recently placed an order for 28 Boeing aircraft, comprising four 777-300ERs and 24 737 Max.
The Chicago-based airline, which disclosed the order in its fourth quarter earnings release, says the order was placed in December 2018.
United did not respond to questions from FlightGlobal, and a Boeing spokesperson referred questions to the airline.
The airline currently operates 18 777-300ERs and 10 737 Max 9s, Flight Fleets Analyzer shows. It has orders for 100 737 Max 10s, four 737 Max 9s and 21 737 Max aircraft where the variant is unspecified.