United Airlines will buy 30 Boeing 757 jetliners and take options on 30 more, Allegis Corp. said Thursday, giving the aircraft-maker its second big order in as many days.

The engine order for the planes went to United Technologies Corp.'s Pratt & Whitney division.Allegis said the total value of the 60 airplanes, engines and spare parts is in excess of $2 billion.

It was the second day in a row that Boeing won a major contract for its fuel-efficient 757 aircraft, sales of which had languished as world oil prices declined. On Wednesday AMR Corp.'s American Airlines said it will buy 50 Boeing 757s and take options on 50 more.

Pratt & Whitney, which lost the American contract to Rolls-Royce Plc, said the engine order by United, which is the biggest U.S. air carrier, was worth $650 million and included 68 engines and spare parts for the first 30 aircraft, and another 67 engines on the optioned jetliners.