With gas prices topping $4 a gallon in some parts of the country, consumers are feeling the pinch at the pump. One way to save money on gas is by using gas rewards cards. Since roughly two-thirds of consumers pay for gas with plastic, according to the National Association of Convenience Stores, it makes sense for many consumers to earn rewards in the process.

Gas credit cards are available as private label cards for specific gas brands or as co-branded cards, which are issued by banks and carry the logo of a payment network such as MasterCard or Visa. In 2010 alone, Americans received 15.9 million offers for private label gas credit cards and 25.4 million offers for co-branded gas credit cards, according to Mintel Comperemedia, a marketing research firm based in Chicago.

Rebate amounts for gas purchases vary, but many cards fall in the 1 percent to 3 percent range, according to the experts paneled for this article. A few co-branded cards offer 5 percent off or more.

Besides the rebate offer, there are a few other factors to consider in choosing a gas rewards card.