United Airlines will introduce its new Boeing 737 Max 9 on domestic routes from Houston Intercontinental and Los Angeles International airports in June.
The aircraft will enter service from the Chicago-based carrier's Houston hub to Anchorage, Austin, Fort Lauderdale, Orlando and San Diego on 7 June. Service will expand to Los Angeles, Sacramento and Tampa on 29 June.
United will also introduce the 737-9 on flights between its Los Angeles hub and Honolulu on 29 June.
"The addition of the Max 9 furthers our efforts to become a more efficient and productive airline," says Andrew Levy, chief financial officer of United, in a statement. "It has better fuel efficiency, lower maintenance costs and does all of this while maximising customer comfort."
The airline will configure its 737-9s with 179 seats, the same density as its 737-900ERs.
United will take delivery of 10 737-9s in 2018, with its first six due in April and May, a securities filing earlier in February shows.
The US Federal Aviation Administration certified the 737-9 on 16 February, clearing the way for the first delivery to Lion Air Group.
United will be the first US operator of the Max 9. However, American Airlines and Southwest Airlines both introduced the Max 8 in 2017.
The mainline carrier has firm orders for 61 737-9s and 100 737 Max 10s.