Alaska Airlines has a no expiration policy for mileage. However (and seemingly in despite of their policy), they can terminate accounts that have no activity in them for two years. They can even reassign your Mileage Plan number to someone else!

Call customer care at 1-800-654-5669 if your mileage account has been closed/expired for a year or less to have them reinstated. If greater than a year, then it is not possible to reinstate them.

$75

American Airlines

Between now and Dec. 31, 2011, American is allowing members to reinstate miles that expired on or after Dec. 31, 2002.

Call 1-800-882-8880 and request AAdvantage account at the main menu

Rates are based on how many miles reactivated: $200+7.5% tax on 1-50,000 miles reactivated; $400+7.5% tax on 50,001-75,000 miles; $600+7.5% tax on 75,001+ miles

Continental Airlines

No expiration policy; soon it will convert to United Airlines’ policy with an 18 month expiration date.

N/A

N/A

Delta Air Lines

No expiration policy beginning Jan. 1, 2011 (although the airline, as they all do, reserves the right to cancel accounts with no activity after sufficient time). This is a relatively new policy. For customers with miles who have expired during 2009-2010, they can be reinstated.

Visit https://buy.points.com/deltaSkyMiles/init.do?method=reinstate

Rates are based on how many miles are reinstated: $25 for 1-10,000; $50 for 10,001-25,000; $100 for 25,001-50,000; $200 for 50,001-100,000; $250 for 100,001 miles or more

Southwest Airlines

Expiration after 24 months of non-activity.

N/A 

N/A

United

Airlines

Miles expire after 18 months of non-activity.

Miles can be reactivated by calling customer service, but only those that have expired within the past 12 months.

The cost varies depending on the amount of miles reinstated. An additional $0.0125 per mile plus a $25 processing fee is added.

US Airways

Miles expire after 18 months of non-activity. US Airways is one of the more expensive airlines to add miles back to one’s account. It is also one of the more generous reward programs offering bargain awards like 110,000 miles for business class to Australia (whereas most airlines charge 150,000 for the same award). The benefits of reinstating miles become more apparent depending on how many miles are being reinstated. If you have around 100,000 miles, you would be crazy not to reinstate and later redeem for a business class ticket to Europe/Middle East/North Asia/Australia. US Airways miles are the best of the best in terms of mileage redemption!

Only expired miles within the last 36 months are eligible to be reinstated, and the policy is that you reinstate them all (not only a portion of them). US Airways offers a unique option (that few people know about) to pay a flat $9 to extend your mileage life for another 18 months. This option is only available if you are within 15 to 17 months of hitting the 18 month mark of mileage expiration. Both options can be completed by calling customer service.

The cost varies on the amount reactivated: $50 for 1-4,999 miles; $100 for 5,000-19,999 miles; $200 for 20,000-49,999 miles; $300 for 50,000-99,999 miles; $400 for 100,000 miles or more.