American Express Co. is steadily building its base of revolving credit card accounts using its Optima brand name, a study by Brittain Associates Inc. has found.

A Brittain study of 6,064 households indicated there are 6.6 million Optima accounts and more than nine million Optima cards in circulation.

It also estimated that three million Optima cardholders routinely pay interest on their balances and owe an average of $1,350 per account.

"As some of the newer Optima portfolios mature, we expect to see the percentage of revolvers increase," said Bruce Brittain, president of the Atlanta-based market research firm. American Express does not release specific Optima figures, but a company source indicated the numbers in the Brittain study seemed low.

The New York card and travel giant is using versions of Optima to pursue targeted market segments of as few as 250,000 to 500,000 people. This is a reversal from the original Optima strategy of 10 years ago when American Express offered it as an adjunct to its charge cards and serious credit problems ensued.

With its revival, "Optima clearly is Amex's way to get into the revolving credit card business, which they hadn't been in," Mr. Brittain said.

"The regular Optima card has been around for several years, but in the last year or two they've taken a very segmented approach and have trotted out various programs."

There are more than a dozen types of Optima cards, for everyone from New York Knicks fans to golfing buffs to Delta Air Lines fliers.

Gail Wasserman, an American Express spokeswoman, said the specialization was a response to market forces.

"Everyone wants to find that one silver bullet where you have millions of customers," Ms. Wasserman said. But "given the competitive nature of the marketplace today and the fact that more consumers are looking for a product that serves their specific needs, there are fewer large niches than there were 5 to 10 years ago."

Mr. Brittain said his survey showed the Optima portfolio is "sort of the same size as the GM/MasterCard portfolio, a bit larger than the Ford/Citibank portfolio." Like those competing cobranded cards, the newer Optima entries enable customers to earn points toward various rewards. The Optima for golfers, for instance, lets cardholders redeem points for equipment, lessons, and even early tee times.

"Most of the people who now carry credit cards-65% or more-carry cards with some sort of added value," Mr. Brittain said.

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