Though not affiliated with WebMiles, I recently applied for a Citibank MasterCard, which is affiliated with American Airlines. With the Gold ($50) and Platinum ($85) level cards, you are granted a credit line, however, should you go over this amount, it is not considered overlimit and not subject to overlimit fees for that given billing period. As long as you pay the amount over your limit by the next billing period, you are exempt from any fees, similar to American Express. If you have a traditional credit card, I too would do what IsleTraveller suggested by submitting on an overpayment to cover the amounts over the credit limit.