Your best bet: an introductory rate you can use this summer. By Joan Goldwasser, Senior Reporter May 12, 2008 As prices creep toward $4 a gallon, a credit card that refunds a percentage of your gas purchases becomes more enticing. But don't be seduced into thinking a rebate will lessen your pain at the pump in a major way. Many cards cap rebates, and some rebates are tiered so that you earn the top amount only for a portion of what you spend.And even though interest rates have fallen like stones, rates on gas-card debt remain notoriously high -- up to 21%. So as summer kicks off, prepare to make the most of your credit cards at the pump. Look for an introductory rate that you can milk this summer. The Chase PerfectCard gives you 6% on gas at any station for 90 days, with a maximum rebate of $30 per month. The BP Visa offers 10% at BP stations only, but throws in 4% on travel and dining expenses, including car rental and hotel stays; the introductory period lasts only 60 days. Chase caps its gas rebate at $15 per month after the first 90 days; BP's card has no cap. With either card, when the introductory period runs out, you will probably be able to find better credit-card deals elsewhere. Advertisement One of the most generous credit cards for gas purchases is the Pentagon Federal Credit Union Platinum Gas Cash Rewards Visa. (If you're not connected to the military, you can become a credit-union member by joining the National Military Family Association for $20 at www.nmfa.org.) The card rewards users with 5% on gas purchases, 2% on groceries and 1.25% on everything else. The Discover Open Road card rebates 5% on gas and routine auto maintenance up to $1,200 a year.