European low-cost operator Norwegian has ordered another 15 Boeing 737-800s, taking to 78 the number it has ordered from the US manufacturer.
The order, announced during the Paris air show, is valued at $1.2 billion.
Norwegian has also firmed its order to buy three Boeing 787s, first agreed in May.
Speaking at the order signing ceremony, Norwegian chief executive Bjorn Kjos said: "It is a fantastic airplane, it is absolutley the best in class. We have to invest in the future and it has the lowest emissions in class to-date."
He also said that he was pushing the airframer to produce an all-new 737 replacement. "Boeing has to build a completely new model with considerably lower fuel burn.
"I am lining up in the queue telling Boeing to build a new aircraft."
He said that the lower fuel burn required is not available with a current narrowbody design, it would have to use more advanced technology, as used on the 787.