Easyjet has agreed to purchase 135 single-aisled Airbus A320s in a deal worth $11.9 billion at list prices.
The carrier claimed its order for 35 A320s and 100 new-generation A320neo planes was made at a "discount".
Delivery of the aircraft is set for between 2015 and 2017.
The deal, which is subject to shareholder approval, was announced at the second day of the Paris Air Show today.
Carolyn McCall, Easyjet's chief executive, said: "All manufacturers competed hard for the Easyjet business. Both Airbus and Boeing offered us new generation aircraft that met our requirements and offered greatly improved fuel efficiency.
"Ultimately, Airbus offered us the best deal, and at a price with a greater discount to the list price than their landmark fleet purchase with Easyjet in 2002.
"This is a great outcome for Easyjet, our shareholders and our passengers, and will ensure that we are able to continue our successful strategy of delivering profitable growth and returns to shareholders."
Easyjet plans to use 85 of the 135 new aircraft to replace existing models. The remainder will form part of the airline's strategy to increase seat capacity by between 3 and 5 per cent each year.
John Barton, the airline's chairman, added: "The new fleet arrangements will enable easyJet to continue its successful strategy of offering customers low fares to convenient airports and efficient and friendly service."
However, Easyjet's founder and largest shareholder Sir Stelios Haji-Ioannou responded to news of the order negatively, saying: “Yet another huge capital expenditure deal with the same supplier at 'secret' prices. Naturally it raises more questions than answers.
“We will ask all our questions when we have seen the full shareholder circular which must include the actual price to be paid for each aircraft and the incremental profit each of these aircraft will actually deliver.”
Easyjet also has an option for another 100 A320neo aircraft.
Graham Smith
