We have used the Priceline gas card and saved a good bit over a period of time.
The stations in our area were the cheaper stations and ones we used anyway. I feel like it is still a savings even at .04 a gallon (10 gallons = 40 cents), every little bit helps. On our list, the average price shown for our area is indeed the average price.
The only thing I don’t like is if you go over the number of gallons that you have paid for, you are charged the retail pump price and a service charge for exceeding the number of gallons.