do you need a costco credit card or just a membership card to buy gas at costco

Yes

Starting July 5th you will need a Costco membership, till then anyone can go.

Costco membership. However use the Costco citi card - get 4% back on your gas purchase.... that could be an extra $300- 500 a year back... or more depending the gas prices and how much you drive..

starting on July 5 you need a costco membership card to buy gas