American Express Cardmembers who pay with any American Express card at participating Dollar locations in the U.S. will receive 10 percent off a rental of any vehicle. The discount applies to time and mileage charges only with at least 24-hour advance reservations. The offer is available on rentals completed by Dec. 31, 2008 and reservations must be made online at dollar.com using promo code AX10. Only a limited number of discounted vehicles are available and some additional charges, holiday and blackout dates may apply.