Robert B. McKinley, director of research at RAM Research, a Frederick, Md., concern that monitors the credit-card industry, noted that about one in five credit cards had an interest rate tied to the prime.

About 38 percent of credit cards issued by banks carry interest rates pegged to the prime, according to Robert McKinley, president of RAM Research.

Among people who maintain a balance on their bank cards, the average amount is $1,700, up from about $400 10 years ago, said Robert McKinley, president of RAM Research in Frederick, Md.

Mr. McKinley of RAM Research said 32 percent of bank card holders paid their bills in full each month, up from 29 percent two years ago.

"American Express is a loser any time any big player comes in offers a card nationally with no fee," said Robert B. McKinley, president of RAM Research in Frederick, Md.

"Mating the tax benefit with the credit card is a good match for them," said Robert McKinley, president of RAM Research, a credit-card tracking company.

"Pay yourself by saving money right away rather than later," said Robert B. McKinley, president of RAM Research in Frederick, Md., which publishes Cardtrak, a monthly listing of well priced credit cards.

Robert McKinley, president of RAM Research, a credit card research company in Frederick, Va., says it's easy to see why companies don't want card holders to pay the entire bill each month.

Those fees annoy consumers, who liken them to paying a cover charge to shop at an expensive convenience store, said Robert B. McKinley, president of RAM Research in Frederick, Md.

RAM Research, a credit-card research company, reports that more than five million establishments around the world accept Visa and Mastercard and about four million accept American Express.