With the nationwide average price for a gallon of regular gas costing nearly $4, the pain of filling up your gas tank might be alleviated a little by using a credit card that pays you something back each time you visit the pump. But choosing a gas-company card could have downsides. For example, credit cards from Citgo, Phillips 66/Conoco, and Shell carry interest rates of 25 percent, which would wipe out any rewards you earned if you don't fully pay off your tab at the end of the monthly billing cycle.
And the rewards offered by gas-company credit cards can be confusing. The Shell card, for instance, offers you 5 cents back per gallon as a credit on your statement, but only if you buy 45 gallons of gas at Shell stations every month. And you don't get back any money once you buy more than 100 gallons from Shell in a month, so your rewards are capped at $60 annually.
One gas-company card worth looking at is the ExxonMobil MasterCard, which gives you 15 cents back on each gallon you buy. At $4 a gallon, that works out to 3.75 percent back—a greater reward than most gas cards offer. Note that the reward counts as a statement credit toward future purchases at ExxonMobil stations.
A general credit card that earns you cash back or points on gas as well as other purchases is the better option if you don't like carrying a lot of cards or if you buy gas at the cheapest station you can find, regardless of brand. The PenFed Platinum Rewards and PenFed Platinum Cash Rewards cards offered by the Pentagon Federal Credit Union pay you unlimited 5 percent cash back on your gas purchases. You will, however, have to jump through some (minor) hoops to join the credit union if you or a relative are not a member of the military, a government employee, or in an affiliated association. You can join PenFed by making a one-time $15 donation to Voices for America's Troops, a military nonprofit group.
The Costco American Express card will earn you 3 percent back on your first $3,000 in annual gas purchases (1 percent back after that). There's no annual fee if you have a Costco membership. If you spend a lot on both gas and groceries, consider the American Express Blue Cash Preferred card. It pays 6 percent cash back on groceries and 3 percent cash back on gas. It carries a $75 annual fee, but there's a $150 sign-up bonus if you spend $1,000 on the card in the first three months. (See The best rewards cards for more information.)
You might also find savings in unlikely places. For example, Walmart credit cards give you a 5-cent-per-gallon discount on each gallon purchased at a Walmart gas station through Dec. 31, 2012. If you're in a part of the country where gas stations are giving a discount for paying cash (generally 10 cents per gallon), a card earning 3 percent back would save you about 12 cents a gallon at the current national average price.
Read How to pay less at the pump for more money-saving tips.