That's 'cause every gas station pays a fee to the credit card companies for the 'privilege' of having customers use their card. Even if you use a, let's say, Citgo card at a Citgo station the owner of that station pays a fee to Citgo (actually whatever card company issues the card for Citgo) to take that card.
The company I work for owns 21 C-stores (6 Mobil, 15 Citgo's) & we're presently starting to unbrand our Citgo stations mostly 'cause the C.C. fees are outrageous (well that & because Hugo Chavez, the pres. of Venezuela (the "owner" of Citgo), can't keep his mouth shut.). C.C. fees just whack the station owners. You'd be surprised at how much we earn on a gallon of gas; 1 to 2 cents p/gallon. C.C. fees, at least for Citgo, are 3 cents per transaction. We don't charge our customers a fee for using their cards. Those that do should be avoided!
The price you pay at the pump is basically set by the distributors, the folks we buy the gas from, plus our jumbo markup of a penny or 2. The price changes more than once a day but we can only change our prices, by law in Wisc., once a day. We actually make more money when the prices are falling 'cause we can keep our margins a wee bit higher (that's the 2 cents day!). When the price goes up & depending on how our nearby competitors are doing there are times when we're selling gas at below what we pay that day. It's usually all a wash simply because we have thousands of gallons underground at any one given time at each station.
That's all I know...I work in the IT Dept. of the company. For the complete story I'd have to spend a couple of hours with our fuel folks & dispatchers. Trust me, fellow gas users, the gas station owner isn't getting rich & unless they have digital signage ($10K - $30K per sign) changing the prices daily in this crappy weather is a job I wouldn't want to do!