NEW YORK:- United Airlines on Tuesday announced multibillion-dollar orders for 25 Airbus and 25 Boeing widebody aircraft in a bid to lower operating costs and expand international destinations.

United said it placed firm orders for 25 Airbus 350 XWB aircraft and 25 Boeing 787 Dreamliners, and taken options for 50 more of each aircraft.

The Chicago-based airline said it was "a significant investment in the company's future with a widebody aircraft order that will enable the carrier to reduce operating costs and better match aircraft to key markets it serves, while providing its customers with state-of-the-art cabin comfort."

United did not disclose financial details of the orders. Commercial aircraft are generally sold at a discount to list price.

John Leahy, Airbus chief operating officer and commercial director, said in a conference call the 25-plane order was worth six billion dollars at list price. He said United had paid less but did not disclose the amount.

The Boeing 787 is listed at an average 166 million dollars on the company's website.

United said the new technology, fuel-efficient aircraft from European aircraft maker Airbus and its US rival Boeing will reduce fuel costs and environmental impact, "while enabling service to a broader array of international destinations."

The airline said it would take delivery of the next-generation widebody aircraft between 2016 and 2019 as it retires its Boeing 747 and 767 aircraft.

The breadth in size and capabilities of the different aircraft models ensures that United has the right aircraft for the right market throughout the fleet replacement cycle, the company said.

"This aircraft order is another significant step on the path to position United for long-term success in a highly competitive global market," said Glenn Tilton, chairman, president and chief executive of UAL Corporation, parent of United.

The 50 new aircraft will reduce the average seat count by about 19 percent compared with the aircraft they will replace, and by about 10 percent when averaged over the entire international fleet, the company said.

Fuel costs and carbon emissions from the 50 aircraft are projected to be reduced by about 33 percent.

Average lifetime maintenance costs for the new aircraft would be approximately 40 percent lower per available seat mile than the aircraft that will be retired, the company said.

The new aircrafts' smaller size, longer range, and lower operating costs will broaden the range of destinations that can be profitably served, the carrier said.

The Airbus 350 has a range 11 percent greater than the current Boeing 747, and the Boeing 787 has a range 32 percent greater than the current B767, it said.

"The increased range of these aircraft will allow us to take full advantage of our well-placed network of domestic hubs, allowing new nonstop service from our hubs to destinations throughout Africa, Asia Pacific, the Middle East and Europe, while improving the economics on international routes we already serve," United said.

United, which serves more than 200 domestic and international destinations, last took delivery of aircraft in 2002, and last ordered aircraft in 1998.

Leahy, the US-born Airbus commercial chief, reiterated a 299 sales target of 300 of the future 350s in 2009. As of the end of November the European aircraft manufacturer had 225 orders on its books.

Firm orders for the 350 XWB stood at a total of 505 on December 4, according to the Airbus website.