One of best deals among VISA, MasterCard and American Express reward cards just got better. As of now all major U.S. air carriers have dropped the mileage expiration requirement from their frequent flyer programs. This week United Airlines announced the change, following a similar announcement by American Airlines last week. The nation's two largest  passenger airlines were the lone holdouts among all U.S. carriers. The recent changes should drive up consumer interest in the bank credit card versions of United and American's frequent flyer programs. Under the former program rules, consumers with annual charge volumes under $10,000 could not cost-justify the higher annual fees associated with United and American's co-branded bank credit card program. However United Airlines said Tuesday that 'Mileage Plus' members' frequent flyer miles will no longer expire, provided the members earn or redeem miles at least once every 36 months. American Airlines also instituted the same requirement last week for members of its 'AAdvantage' program. A qualifying activity, to keep miles active includes taking a paid flight on the carrier or its affiliates; or making a purchase with the carrier's co-branded VISA or MasterCard; or staying at a partner hotel; or renting from a rental partner; or accepting a special mileage offer from the carrier. United also announced Tuesday it will  reinstate 1998 expired miles to members who register and take either two paid domestic roundtrips or one paid international roundtrip on flights operated by United, United Shuttle or United Express.  Under the new guidelines, all miles in a Mileage Plus member's account through 1999 will be valid until Dec. 31, 2002 and will expire on that date only if a member has no qualifying activity between Jan. 1, 2000 and Dec. 31, 2002.  As of Jan. 1, 2000, a new 36-month non-expiration period will begin each time a member has qualifying account activity by earning or redeeming miles. Information on mileage reinstatement and registration will be available tomorrow at offers.mileageplus.com/mpw049 or by calling 1-800-645-4502 (enter promotion code 49). For more details on the American Airlines AAdvantage program changes visit www.aa.com or call 1-800-882-8880.