Budget carrier Ryanair is ordering another 25 Boeing 737 Max 8s, taking its overall commitment to 135 of the re-engined twinjets.
Boeing had previously attributed the aircraft to an undisclosed customer.
Ryanair had ordered 100 firm 737 Max 8s in 2014 – along with 100 options – and subsequently ordered a further 10 during last year's Paris air show, although it retained its 100 options.
But the latest order for 25 represents the conversion of 25 of the carrier's options. Ryanair says it will hold 75 options on the 737 Max as a result.
The airline is to receive its first Max in spring next year.
Ryanair's new agreement for the 197-seat aircraft is worth $3 billion at catalogue prices, says Boeing. It takes the airline's 737 orders to more than 650.
All 737 Max jets are powered by CFM International Leap-1B engines.