The parent of United Airlines, which held unsuccessful merger talks with Continental Airlines, said it would pursue all options to ensure a sustainable future.

"Ensuring you have the right partner is everything," UAL said in a statement. "We will pursue all options to ensure a strong, sustainable future for our airline and will not shy away from the tough choices necessary to create value for our shareholders."

Earlier on Sunday, Continental said it had decided against merging with any other airline, but will explore alliances with other carriers.

Continental had called off talks with United due to the other carrier's weak financial condition, and "the increasing cost of oil increases the risk of doing an airline merger," a source briefed on the matter said.