BY SUSAN CAREY AND DANIEL MICHAELS

UAL Corp.’s United Airlines confirmed Tuesday that it placed initial firm orders for 50 wide-body planes, evenly split between Boeing Co.’s 787 Dreamliner and rival Airbus’s new A350 model, and arranged future purchase rights for 50 more of each.

United, the third-largest U.S. airline by traffic, hadn’t ordered new aircraft for 11 years. The carrier began shopping last summer, figuring it could drive a better bargain by pitting the manufacturers against each other at the bottom of the business cycle. The airline hired aviation-consulting firm Seabury Group LLC to help it negotiate.

At catalog prices, the order is valued at …