BudgetTravel

Until recently, reward miles for US Airways and United didn't expire until there had been three years of no activity. Under new policies, miles will be deleted if an account is stagnant for 18 months. That's not to say you must actually fly within the allotted time to keep miles alive. The key word is activity.

Most airline reward programs have online malls with links to dozens of partner businesses where you probably already shop, including Barnes & Noble, Gap, Old Navy, Target, and Starbucks. You can keep existing miles from expiring--and earn miles for every dollar spent--by logging in at the airline's site with your frequent-flier number and making a purchase through a linked retailer. That's hardly the only method for saving miles, however. Signing up for an airline-affiliated credit card, or using one that you already have, also qualifies as account activity. So does trading in reward miles for hotel stays, car rentals, or magazines; taking an airline's online quiz; or answering follow-up questions after watching advertisements on your computer arranged through online marketers E-miles or E-rewards.

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We've examined policies for eight domestic carriers and found many, many options for saving miles. In the chart at right (click to see the full chart), "Our Pick" is an especially easy way to keep reward points from disappearing--in some cases, you won't have to spend a dime. We're including each carrier's shopping partnership links because they're tougher to find than you'd imagine.

To purchase through some partner retailers, you must not only sign in with your frequent-flier number but also type in a special code before buying, as explained in the airline program's online mall. Pay close attention to detail to make sure that your account is credited. Within a few weeks, log in to your reward program account to check that the "activity" has been noted.

American Airlines

• Credit Card: Citi AAdvantage MasterCard, free first year, $50 annually thereafter; 15,000 bonus miles after you spend $250
• Shopping: aadvantageeshopping.com (240 partner retailers)
• Our Pick: Two bags of coffee via Starbuck's retail website, StarbucksStore.com. ($9.50)
  Correction: In the original article and the accompanying chart, we erroneously said that a participant in American Airlines' reward program could keep their account active by buying a gift card from partner Starbucks.

Continental

• Credit Card: Continental Airlines World Master-Card, $85 annually; 15,000 bonus miles with first purchase
• Shopping: continental.com/for/shoponepass (50 partner retailers)
• Our Pick: A year's subscription to music magazine Blender (400 miles)