Irish lessor Avolon has signed a memorandum of understanding for 75 Boeing 737 Max 8s at the Paris air show.
Boeing says the aircraft, which have a list-price value of $8.4 billion, will be delivered from 2021.
The deal also includes an option for a further 50 Max 8s, and brings Avolon's total "owned, managed and committed" fleet to 925 aircraft, Boeing says.
In March, the HNA Group-owned lessor delivered the first Max 8 to launch operator Malindo Air.
"This order represents the single largest order that Avolon has placed with Boeing to date and underlines the scale of our ambition and the strength of our business," states Avolon chief executive Domhnal Slattery. "Our strategy is to maintain an industry-leading portfolio of young, modern and fuel-efficient aircraft."
Flight Fleets Analyzer shows that Avolon has one Max 8 in service and a further 40 on order. It also has 10 Max 9s on order, along with seven Max jets of an undisclosed variant.