Southwest Airlines has placed a firm order for 150 Boeing 737 Max aircraft - valued at $19 billion at list prices, the largest firm order in Boeing's history - and will become the launch customer for the re-engined narrowbody.
The carrier is the first customer to place a firm order for the 737 Max.
The Dallas-based airline, which was also the launch customer for the Boeing 737 Next Generation series, will take delivery of its first 737 Max in 2017.
Alongside the firm order for 150 737 Max aircraft, Southwest has also firm-ordered an additional 58 737 Next Generation aircraft. Of these, 25 were existing options.
The new orders increase Southwest's firm orders with Boeing to 350 aircraft, scheduled for delivery between 2012 and 2022.
Southwest has substituted 737-800s for all 737-700 deliveries scheduled for 2012 and 2013, in addition to a portion of its 2014 deliveries. It has also taken 150 737 Max options, the carrier said.
Its Max order includes the flexibility to accept the -7 or -8 variants.
"Today's environment demands that we become more fuel-efficient and environmentally friendly, and as the launch customer of the Boeing 737 Max, we have accomplished both," said Southwest chief executive Gary Kelly.
Boeing said 13 customers have now ordered more than 900 737 Max aircraft. On 12 December it set a list price of $77.7 million for the 737 Max -7, $95.2 million for the -8 and $101.7 million for the -9 variant.