Canadian carrier WestJet is intending to order 65 Boeing 737 Max twinjets for delivery from September 2017.
The airline says it has agreed, through a letter of intent, to take 40 Max 8 and 25 Max 7 variants.
All the aircraft will be fitted, as standard, with CFM International Leap-1B engines.
"This pending order reinforces our strategy of maintaining the flexibility in our fleet plan while enabling us to introduce new fuel-efficient technology and enhance our inflight guest experience," says WestJet chief Gregg Saretsky.
"Our strong balance sheet allows us the opportunity to support our low-cost business model and contribute to our profitable growth through the renewal of our fleet with a lower operating cost aircraft."