United is the only airline that lets fliers, with a prepaid card starting at $5,000, buy into elite status without flying a single mile. Elites at risk of losing their status can enroll in a $499 program that doubles subsequent miles earned.

Key markets: Chicago, Denver, Los Angeles, San Francisco, Washington

Elite miles: Premier (25,000), Premier Executive (50,000), 1K (100,000)

Pros: United sells 500-mile upgrade coupons in $200 four-packs. Elite members stuck in coach on full flights get priority seating in the front rows, where 5 extra inches of precious legroom await.

Cons: Even top-tier customers aren't promised upgrades when seats are available; they must trade in coupons to move up a class. United has scant special airport security lanes.