Boeing and United Airlines have finalised an order for up to 75 787 aircraft.
The order for 25 firm 787-8s and an additional 50 options are set to begin delivery around the time United begins retiring its international 767 and 747-400 fleets around 2016.
The order is valued at $4.2 billion in average list prices.
John Tague, president of United, says in a statement that the airline's Boeing 787 order represents a substantial investment in our future and will enhance the significant progress we are making in improving the global competitiveness of our company while providing the opportunity to open new profitable markets and serve a broader range of international destinations."
The order was first announced on 8 December 2009 as part of a deal that included up to 150 aircraft split with the Airbus A350-900.
Boeing has amassed orders for 876 787s from 57 customers.
Entry into service with of the 787-8 from launch customer Japan's All Nippon Airways is expected in the fourth quarter of 2010.