The companies had negotiated since August, when creditors pushed AMR to conduct merger talks so they could decide which earned them a better return: a merger or an independent American.
The deal would need approval by AMR's bankruptcy judge and antitrust regulators, who have permitted three other big airline mergers to go ahead since 2008.
The rapid consolidation has allowed the surviving airlines to offer bigger route networks that appeal to high-paying business travelers. And it has allowed them to limit the supply of seats, which helps prop up fares and airline profits.
The new American would have more than 900 planes, 3,200 daily flights and about 95,000 employees, not counting regional affiliates. It will be slightly bigger than United Airlines by passenger traffic, not counting regional affiliate airlines.