United orders 40 Boeing planes

United Airlines on Thursday said it had ordered 40 new 737-700 aircraft from Boeing.

United said the order of the 150-seat aircraft, worth in total about $3.2 billion by book price, will enter service in mid-2017.

They will replace the some of the capacity currently served by smaller, 50-seat aircraft operated by United's regional partners.

"Our customers have a preference for an improved travel experience, including first-class seats, Economy Plus, and wi-fi. These aircraft are an efficient way to met those needs while reducing 50-seat flying," said United's acting chief financial officer Gerry Alderman in a statement.

United parent United Continental Holdings reported a 2.7 percent decrease in operating revenues for 2015 to $37.9 billion, due to lower passenger unit revenues.

But operating net income more than doubled to $5.2 billion helped by a plunge in fuel costs.

Net annual income increased more than sixfold, to $7.3 billion.

But full-year adjusted earnings of $11.88 per share missed market estimates of $12.00.

Shares in United dropped 1.1 percent to $44.63 in pre-market trade.