American Airlines has firmed up options on two Boeing 777-300ERs to support international growth.
The aircraft will be delivered in late 2012.
American's existing fleet of Boeing 777-200ERs is powered by Rolls-Royce Trent 800 engines, but the newly-ordered 777-300ERs will be powered by General Electric GE90s.
Boeing Commercial Airplanes president Jim Albaugh says: "American is the first carrier in the US to order the 777-300ER. These new airplanes will complement their large fleet of 777-200ERs offering additional flexibility in serving the nonstop routes, while providing increased efficiency and reliability."
AMR president Tom Horton adds: "The seating capability of the aircraft will give us growth flexibility in slot-constrained airports and provide us with greater ability to serve new long-haul markets."