What's the difference between a gas credit card and a co-branded credit card of a particular gas station?

A co-branded card means is that a credit card is issued by a financial institution in partnership with a particular merchant. This could be a department store, an airline, a hotel chain, or a fuel company. The highlight of co-branded cards is that they come with special discounts and features for the customers of a certain brand. If you have a co-branded credit card, you will earn rewards when you use it at the merchant or retailer that issued it. You can also use it to make purchases anywhere, in most cases, but the biggest rewards will be reserved for the brand that is on the card. A gas credit card is usually issued by a gas company such as Shell, Exxon, or Amoco. Otherwise, you can use a general rewards card that offers cash back. There are some that offer more cash back at gas stations than other places, so one of those would be of most interest to you, if you don't want to be committed to using one particular gas station to fuel up your vehicle.