You might assume that gas station credit cards offer the best deal on filling your tank. That seems to make sense, because why wouldn't the company selling the gas offer the best perks to customers using its branded credit card?

The reality, however, is very different. An average gas station credit card charges an interest rate of 23.61%, almost 7 percentage points higher than the national average across all general purpose credit cards, according to a new analysis of 28 widely available gas cards. In addition, the study showed that the rewards offered by gas station credit cards don't measure up to those offered by general purpose cards.

A gas pump

A gas station credit card may not be your cheapest option for filling up. Image source: Getty Images.

How do gas station cards measure up?

The gas station credit cards in this survey offer per-gallon discounts averaging $0.05 per gallon. If you consider that the national average for a gallon of gas is $2.66, according to AAA, then $0.05 per gallon is just under a 2% return.

If you live in a state where gas costs more, the numbers are even worse. In California, the survey noted, the average price per gallon of gas is $3.52. So a $0.05 per-gallon discount comes out to a less than 1.5% return.

It's easy enough to find general purpose credit cards that offer 2% rebates on gas and other purchases. In general, according to, those cards will also charge lower interest rates and they may offer other perks like sign-up bonuses. And you can't overlook the fact that a gas station credit card is generally limited to use at that gas station chain.

Gas station cards, however, can be a good deal in one situation, according to the folks at Twelve of the 28 cards analyzed offer an introductory perk -- most commonly $0.25 off per gallon for two or three months.

"If you're planning a big road trip, this is one instance when it might make sense to sign up for a gas rewards credit card," said senior industry analyst Matt Schulz. "But even then, there are restrictions to be aware of -- several of the most generous introductory offers are capped around $100 of fuel credits. You're probably still better off with a general cash-back card."

Protect your credit

Gas station and store-specific cards, in general, can be tempting because they're generally easy to sign up for. In many cases, you can get one instantly at checkout and put off having to lay out cash or adding to a balance on another card. It's important to remember, though, that these are still credit cards.

"A gas card basically hits your credit the same way any other card would.," Schultz said in an email exchange with The Motley Fool. "It can be a good tool for helping someone build credit from scratch or rebuild crummy credit simply because they might not be able to get other types of cards. They just need to make sure they pay their balances off quickly because otherwise the high interest rates can be a real problem."

Schultz is also in favor of retailer-specific cards, but he laid out a precise scenario where using one makes sense.

"Retail cards can be great if you're a frequent customer who pays your balance off each month and the card offers rewards that you can't get from general-purpose cards," he said. "Beyond that, you're probably better off with a general-purpose card."

The key to any credit card is paying off your balance each month. Not doing so will offset or eliminate any rewards you earn. That makes gas cards, with lower rewards and higher interest rates, generally not a smart play for most consumers.