United Airlines frequent flyer miles will no longer expire

United Airlines is changing its frequent flyer plan so that miles accrued don't expire in a member's lifetime.

Wednesday's change to MileagePlus aligns United's program with those of Delta Air Lines and JetBlue Airways. Delta changed its mileage expiration policy in early 2011.

American Airlines Group Inc., the world's largest carrier, requires members to earn or redeem miles at least once every 18 months, as had United. Southwest Airlines Co. and Alaska Air Group Inc. require account activity at least once every two years.

The more generous policies reflect efforts to make airlines' co-branded credit cards - and the miles attached to spending on them - more attractive to travelers. Big issuers such as JPMorgan Chase & Co. and American Express Co. are a critical source of revenue for U.S. carriers.

Airlines must count frequent flyer miles as a financial liability on their balance sheets. That gives carriers an incentive to encourage program members to use the miles, including for items other than air travel.

"We want to demonstrate to our members that we are committing to them for the long haul, and giving customers a lifetime to use miles is an exceptionally meaningful benefit," Luc Bondar, United's vice president of loyalty, said in a statement.