USA Today did a good job in compiling the expiration policies of major U.S. frequent flier programs. Time to strategize your usage of mileage programs!

Of 16 U.S. airlines contacted by USA TODAY, only Continental and Aloha said miles do not expire in their frequent-flier members' accounts. Continental has a written policy stating that miles can expire if none are earned in 18 months, but the airline doesn't act on it, says spokesman David Messing.

AirTran and JetBlue have the strictest expiration policies, with credits or miles expiring one year after they are earned.

Airlines' expiration policies have nuances. For example, some carriers require miles be added to keep accounts alive. For others, adding or redeeming miles will keep the account alive.

Members of many airlines' frequent-flier clubs can prevent their miles from expiring by cashing some in for a magazine subscription. Or they can make an online purchase from a retail store that's affiliated with an airline and provides bonus miles.

The moves by airlines to tighten mileage expiration policies may not stick, says Andrew Watterson, of Mercer Management Consulting.

"Like airline prices, mileage expiration policies seem to go up and down based on the strength of the travel market," the airline consultant says. "It wasn't long ago when airlines were competing to lengthen the expiration period."