Passengers check-in for flights with United Airlines at O'Hare Airport.

United Continental on Thursday said it expects a higher pre-tax profit margin for the just-ended third quarter than it had previously forecast, thanks in part to extra revenue from a credit card agreement for frequent fliers.

The Chicago-based airline said its pre-tax margin will be between 16 percent and 17 percent, compared with a prior forecast of between 13.5 percent and 15.5 percent, excluding special charges. That reflects about $100 million in revenue from changes to marketing agreements with JPMorgan Chase's Chase Bank USA and Visa's U.S. subsidiary.