Canada's second-largest airline, Westjet, placed a tentative order on Thursday for 65 Boeing 737 aircraft, which it said it would firm up next month.
The purchase is estimated to cost Can$6.3 billion.
WestJet's current fleet consists of 103 Boeing Next-Generation 737, and four Bombardier Q400 NextGen aircraft.
Including this pending order, WestJet's future Boeing 737 aircraft deliveries total 92, with commitments for the proposed Boeing 737 MAX 7 and MAX 8 aircraft, scheduled for delivery from 2017 through 2027.
The Max 7 and 8, the airline said in a statement, will reduce fuel burn and CO2 emissions by 13 per cent as compared with the most fuel-efficient single-aisle aircraft currently available.
Boeing currently has firm orders from five other airlines in North America for its 737 MAX aircraft.