The benefits of shopping at Costco with a TrueEarnings Costco American Express card include cash back when buying gas and a special cash back voucher for use at Costco stores, as of April 2015. Other benefits of shopping with a regular American Express card include buyer protection and special offers.
By signing up for a TrueEarnings Costco American Express card, the cardholder gains access to both the regular set of benefits that come with an American Express card as well as special privileges available only at Costco stores, such as the ability to use the card to pay for purchases. Many Costco stores only allow for payments in the form of either cash or a debit card and thus prohibit use of major credit cards. However, Costco does allow its members to use American Express cards to pay for purchases.
Any purchases made on a Costco American Express card also earn the cardholder a cash back reward calculated as a percent of the transaction total, with the actual amount varying based on the type of purchase. For example, cardholders purchasing gasoline earn cash back at a different rate than if they use the card to pay for a restaurant bill.