Costco only accepts Visa-branded credit cards in its warehouses. However, Costco.com and Costco app shoppers can also pay with Discover or Mastercard in addition to Visa. Costco also accepts mobile wallets, checks, EBT cards, and cash for in-store purchases. Costco gift cards can be used as a workaround for using other credit cards for purchases. Its important to note that Costco does not accept American Express, Discover, or Mastercard credit cards in its warehouses.