United Airlines has placed an order for 150 Boeing 737s, including 100 of the re-engined 737 Max 9.
The order, which includes 50 current generation 737-900ERs, takes the 737 programme past 10,000 orders overall.
Boeing says the deal is worth $14.7 billion at list prices.
United becomes the North American launch customer for the CFM International Leap-1B-powered 737 Max 9.