Long-haul low-cost operator AirAsia X is ordering 25 more Airbus A330-300s, taking its firm orders for the type to more than 50.
Another six of the type will be leased from ILFC.
AirAsia X had previously indicated that it would sign a major fleet deal with the airframer today. The order includes the latest longer-range version.
Airbus states that the agreement is the largest A330 order covered by a single purchase deal.
AirAsia X, which is also a customer for the A350, will start taking delivery of the additional A330s in 2015. It has ordered a total of 51.
"This order stamps our firm intent to dominate the long-haul, low-cost carrier space and marks the next phase in our development to be the undisputed global market leader," says the carrier's co-founder Tony Fernandes.
AirAsia X has not given an engine selection for the jets but its fleet is primarily fitted with Rolls-Royce Trent 700 powerplants.
It operates 16 A330-300s and has 10 A350s on order.