Boeing has announced an order by United Continental and its wholly owned subsidiary, United Air Lines, for 150 737 airplanes, including 100 of the new 737 MAX 9.

United, the largest airline in the world by traffic, is the latest carrier to choose the newest member of the 737 family, which today eclipsed 10,000 orders overall.

The deal, worth $14.7 billion at list prices, also includes 50 Next Generation 737-900ERs (Extended-Range).

“This order is a major step in building the world’s leading airline, and we look forward to offering our customers the modern features and reliability of new Boeing airplanes, while also making our fleet more fuel efficient and environmentally friendly,” said Jeff Smisek, United president and chief executive.

“New aircraft deliveries support our flexible fleet plan, permitting us to tailor future capacity up or down, based on changes in demand or other market conditions.”

United is the North American launch customer for the 737 MAX 9.

The order continues the momentum for the 737 MAX, which now has more than 1,200 orders and commitments from 18 customers.

Counting all variants, the 737 program now stands at 10,039 orders, further cementing the 737 as the undisputed best-selling jetliner in the world.

The 737-900ER and 737 MAX 9 ordered by United can seat up to 180 passengers and feature the new Boeing Sky Interior.

The sleek interior boasts modern lines, a spacious cabin with more headroom and LED lighting that offers vibrant color options.

United Airlines and United Express operate an average of 5,605 flights a day to 375 airports on six continents. In 2011, United flew more than two million flights that carried 142 million passengers, more than any other airline.