United Airlines has placed a major order for Boeing’s new 737 MAX 10 aircraft, which was unveiled by the US planemaker this week.

The deal, which was announced at the Paris Air Show, will see United convert 100 of its current 737 MAX orders into 737 MAX 10s, instantly making it the largest 737 MAX 10 customer in the world.

The 737 MAX 10 is the new high-capacity version of Boeing’s popular single-aisle jet. It can seat up to 230 passengers in a single-class layout, or 188 in a typical two-class configuration.

United also announced an order for four additional Boeing 777-300ER aircraft.

“The 737 MAX 10 will enable us to continue using larger and more efficient aircraft within our domestic network and better meet the needs of our customers today and into the future,” said Andrew Levy, United’s executive vice president & chief financial officer.

United expects to begin taking delivery of its 737 MAX 10s in late 2020.