Turkish Airlines has announced an order for 15 Boeing 777-300ERs plus five options.
Three of the aircraft will be delivered in 2014, followed by seven in 2015, five in 2016 and five in 2017. Boeing's list price for the order is approximately $6.3 billion.
The Turkish flag carrier has been playing up the prospect of orders with both Boeing and Airbus in recent weeks.
It signed an agreement with Airbus for 15 A330-300s in early October, which would give it 27 of the type by the time deliveries are completed in 2016.
Chief executive Temel Kotil also told Flightglobal in September that he is considering placing orders for A380s and 747-8s, though he said adding twin-engine A330s and 777s is the immediate priority.
Separate discussions centre on the possible introduction of the 737 Max and A320neo to gradually replace the airline's narrowbody fleet.
Turkish Airlines operates a fleet of 174 aircraft, according to Flightglobal's Ascend Online database, comprising 12 777s, 21 A330s, seven A340s, 75 A320-family jets and 59 737s.