United Airlines ordered 24 additional Boeing 737 MAX jets and four more 777-300ER aircraft last year.
The $4.5 billion order, according to list prices, was booked as unidentified on Boeing’s Orders & Deliveries website.
The Chicago-based airline has steadily placed new orders for the two Boeing aircraft to serve its large domestic and international network.
United Airlines is among the more than 100 customers who have made the 737 MAX the fastest-selling aircraft in Boeing history, receiving more than 5,000 orders since the program’s launch.
The 737 MAX has more range and 14 per cent better fuel efficiency compared to today’s aircraft and 20 per cent more than the model it replaces.
The 777 has become the best-selling twin-aisle jet family in history, earning more than 2,000 orders. In fact, United’s order pushed the program over the 2,000 threshold in December.