Boeing on Tuesday announced that Ryanair has committed to order 175 Next-Generation 737-800s for the airline’s fleet expansion.

When finalized, the agreement will be worth $15.6 billion at list prices and will be posted to the Boeing Orders & Deliveries website as a firm order.

“This agreement is an amazing testament to the value that the Next-Generation 737 brings to Ryanair,” said Boeing Commercial Airplanes President & CEO Ray Conner. “We are pleased that the Next-Generation 737, as the most efficient, most reliable large single-aisle airplane flying today, has been and will continue to be the cornerstone of the Ryanair fleet. Our partnership with this great European low-cost carrier is of the utmost importance to everyone at The Boeing Company and I could not be more proud to see it extended for years to come.”

Ryanair is Europe’s leading low-cost airline and is based in Ireland.