SAN FRANCISCO, July 16 (Xinhua) -- United Airlines (UAL) announced Monday that it has placed an order for four more new Boeing 787-9 Dreamliners to expand its fleet with more fuel-efficient planes.

The U.S. airline said the latest purchase for the new airplanes, valued at about at about 1.1 billion U.S. dollars, is part of its widebody fleet replacement strategy.

"We will continue to roll out new announcements in the future as we implement our comprehensive fleet plan," said Gerry Laderman, UAL's senior vice president of finance.

As the world's third-largest airline by revenue, UAL said it expects to take delivery of the four 787-9 variants in 2020.

The 787-9 Dreamliner's manufacturer, Boeing Corp., said the new model is the longest-range version of the 787 family that can fly up to 14,140 kilometers with 20 percent less fuel than older generation jets.

With this latest purchase, UAL has now ordered 55 787 Dreamliners. Nearly half of all 787 customers have placed repeat orders for the airplane, according to Boeing.

UAL also announced an order for 25 new E-175 planes from Brazil's major aircraft maker Embraer SA, to replace 25 CRJ-700 aircraft flown currently by its United Express partners. It hopes to receive the Embraer E-175 aircraft in 2019.