Bob C,
Some stations charge more if you use a credit/debit card (not all, and not most, but some), otherwise there is no difference in price using a credit card, a debit card, a prepaid card or cash???...assuming you pay off the credit card balance each month.
It's easier to simply pay cash, or just not use gas stations that charge extra for using credit/debit cards. I know charging extra for using plastic is a common practice in the New York area, and in some other major cities around the US. There are even some gas stations in the Dallas area that charge extra for using plastic...you just have to look for the signs they are required to post that tell you they charge more for using plastic.
Some grocery chains in the area will charge you less for gas if you use their prepaid credit card, or Wal-Mart will charge less if you pay with a Wal-Mart credit card.
I usually use my debit card to buy gas, but only at stations that do not charge extra for using credit/debit cards.
If you really want to save gas money, log onto www.gasbuddy.com, become a member and log in gas prices as you spot them. They can desplay the cheapest gas prices in your area, or any area by zip code. If you are planning a trip, they will map on your route and tell you were to gas up at the lowest prices stations along your route. If you have a smartphone with a GPS, they can even tell you the gas prices in the area where you are at any moment in time.
...Rich