In general I don't recommend purchasing airline miles, even at a discount, but if you have an immediate need for miles for a high value award, it can make sense. If you have a Citi Premier or Citi Prestige card and a few ThankYou points in your account, you can buy miles indirectly through the ThankYou Rewards program at a cost of only 2.5 cents per mile (or less when transfer bonuses are in effect). The best airline programs for these indirect mileage purchases, in my opinion, are: Air France, Cathay Pacific, Singapore, and Virgin Atlantic.