Gas station cards as well as Costco etc are affinity cards or branded cards. These companies are not banks but a partnership through an existing bank (Citi, Wells, Chase, etc) Shell may offer the card but it's backed and serviced by Citibank. They may be designed to help with discounts on fuel purchases but don't help in many other areas. We like Discover because of the large cash back rewards. We use it for just about every single thing we buy and pay it off at the end of the month. The cash rewards can be used toward the bill itself or credit for purchases. Most of our Amazon purchases are free because they allow us to apply credits there.