You must have a Costco membership card to use the gas pumps. Then it will accept credit, debit cards. There is usually a Costco employee there to help pump gas, assist with any problems, answer questions

Membership is $50 annually

If you avail yourself with the benefit of a more discounted gas for your vehicle, you should apply for membership costing you $60.00/annually (I think if I'm not mistaken) plus right now you can only use visa credit card for gas while purchases not gas can be paid with either cash or your visa card.