British Airways on Monday announced a deal to buy up to 36 long-haul Airbus A350 passenger planes worth almost $12.0 billion at list prices.
BA said parent group IAG, which owns also Spanish carrier Iberia, had signed a Memorandum of Understanding to buy 18 Airbus A350-1000 aircraft with an option to purchase 18 more.
Each plane has a catalogue price of $332.1 million, according to European planemaker Airbus' website, though airlines tend to receive significant discounts on bulk orders.
"After a thorough selection process, International Airlines Group (IAG), and British Airways have signed a Memorandum of Understanding (MoU) to buy 18 Airbus A350-1000 aircraft plus 18 options, as part of the airline's on-going long-haul aircraft fleet renewal and modernisation strategy," a statement said.
"IAG, owner of both British Airways and Iberia, has also secured commercial terms and delivery slots that could lead to firm orders for Iberia. Firm orders will only be made when Iberia is in a position to grow profitably, having restructured and reduced its cost base," it added.
IAG chief executive Willie Walsh said adding the A350-1000 to BA's fleet would "bring many benefits."
He added: "Its size and range will be an excellent fit for our existing network and, with lower unit costs, there is an opportunity to operate a new range of destinations profitably. This will not only bring greater flexibility to our network but also more choice for our customers."
Earlier this month, IAG said it had reached an agreement with Airbus' US rival Boeing to buy 18 of its 787 Dreamliners.
The move is a show of confidence in the plane, which was grounded around the world in January owing to problems with its battery system.
IAG meanwhile plunged into an annual net loss of 943 million euros in 2012 on severe financial strains at its Spanish arm Iberia and owing to a soaring fuel bill.
IAG is cutting more than 3,800 jobs at Iberia as the airline struggles as a result of Spain's weak economic backdrop.
BA and Iberia merged in January 2011 in a tie-up aimed at slashing one another's costs, as a sharp economic downturn and rise of low-cost competitors sparked steep losses for traditional carriers.