American Express's Costco Credit Card helps save me money on gas because the gas price at Costco is almost alway the lowest. Plus the Costco Credit Card gives me a percentage back on all purchases, making the price of the gas even lower. You can also use the card anywhere American Express is accepted, which increases your Costco rebate check. Remember, when using any credit card, don't buy anything you can't pay for when the bill comes. Having to pay interest on your purchases will wipe-out all of your savings and more.