I just received an email from USAA about their new USAA Cash Rewards Plus Amex credit card offering 5% cash back on gas purchases up to $3,000 in spend each year (you also get 2% at the grocery store and 1% on everything else). There’s no annual fee on the card.
It’s only available to USAA members, or to people who have military in their family (you’ll see who qualifies when you click through the link). It is the best no annual fee card out there for gas cash back. I wouldn’t use it for anything else, but the $3k cap is reasonable for most people, and with no annual fee you can keep it open forever to help with your credit score (open unused credit & the length you’ve had credit open both help your score).
Application (not affiliate) here.