Turkey's Pegasus Airlines plans to place an order for 100 single-aisle aircraft in February 2012 and is considering both the Airbus A320neo and the Boeing 737 Max.
The airline signed a contract five years ago for 40 Boeing 737-800s.
"Now we must reshape the fleet after 2016. The 40th aircraft will be delivered in 2016 and we need 100 aircraft for the future of Pegasus Airlines," said Pegasus general manager Sertac Haybat.
He added: "We are talking with Boeing for the 737 Max and Airbus for the A320neo. Fuel efficiency is the key element for us for better costs."
Pegasus plans to grow by a minimum of 10% each year.
The A320neo is due to enter service in 2015, with the 737 Max scheduled to follow in 2017.
Haybat said: "If we get slots for 2018 and beyond, Pegasus also will think about leasing some more aircraft."