Singapore Airlines will commit to purchase 20 777-9s and 19 787-10 Dreamliners from Boeing.
The national carrier and 787-10 launch customer also recommited for its previous order for 30 787-10 airplanes.
"Singapore Airlines has been a valued Boeing customer for more than 50 years and we are honored they have selected the 777X and additional 787-10s to expand its future widebody fleet," Boeing Commercial Airplanes President and CEO Kevin McAllister said. "They are the most efficient, capable and passenger preferred airplanes in their class. We appreciate the trust, commitment and endorsement of Singapore Airlines, and look forward to delivering market-leading capability to one of the world's most widely respected industry leaders."
Advanced technology including a new composite wing, all-new engines and superior aerodynamics will result in the incredible fuel efficiency promised by the 777X family, officials said.
The 777-9 will be the largest and most efficient twin-engine commercial jet in the world with the lowest operating cost per seat of any commercial airplane and no competitor in its market segment, they said. The 787-10 is the third member of 787 Dreamliner family.
When finalized, the order will be posted on the Boeing Orders and Deliveries website.