United Airlines announced Wednesday it is ordering 370 Boeings 737s and 757s with a price tag of $15.78 billion, the largest aircraft purchase in U.S. history.

United Chairman Stephen Wolf said the 737s - models 300, 400 and 500 - will be equipped with General Electric CFM-56 engines. He said United will place 120 orders for the 737s with options for another 130.Wolf said the airline also will place firm orders for 60 Boeing 757s with options for another 60, all to be equipped with Pratt and Whitney 2037 engines.

Delivery dates range from July 1, 1991, to February 1996.