Boeing said it had finalised an order for 150 777X planes from Dubai's Emirates Airline in a deal valued at $56 billion at list prices.
The deal includes purchase rights for an additional 50 airplanes that, if exercised, could increase the value to about $75 billion at list prices, Boeing said in a statement on Wednesday.
Last month, Emirates scrapped a $16 billion order for 70 Airbus A350 widebody aircraft.
The 777X, launched at the Dubai Airshow in November, is the latest version of Boeing's best-selling widebody jet, a so-called mini-jumbo, which carries a list price of up to $320 million.
The current versions are capable of seating up to 550 passengers in a single-class configuration, according to Boeing. In a more typical three-class configuration, the jet family seats up to 386 passengers and has a range of up to 9,395 nautical miles.