American Express Co has formed a joint venture with the French luxury shopping site, which will expand the lender's e-commerce business while opening the web site to American consumers.

Ownership of the new venture will be equally split between American Express and, the companies said on Thursday. Further financial details were not disclosed.

The venture is another step in American Express's effort to gain more business from processing the transactions of wealthy customers, especially via new technology like online and mobile commerce. The credit card company lends directly to consumers, but it also competes with Visa Inc and MasterCard Inc to process credit card transactions for banks.

Last year, American Express hired longtime mobile executive Dan Schulman to lead its technology expansion efforts.

Schulman said in the announcement that AmEx was attracted by's heritage in the luxury market and emphasis on customer service.

Like Gilt Groupe in the United States, sells designer goods at discount prices to members of its web site. Such sites allow fashion houses to sell excess inventory at large discounts without damaging their brand, by selling to a limited group of people.

Launched in 2001, says it has about 13 million members and has sold more than $1 billion worth of goods to European consumers. Private-equity firm Summit Partners bought a 20 percent stake in the company in 2007.

American Express shares were down about 1 percent to $49.32 in late Thursday morning.

(Reporting by Maria Aspan; editing by Gerald E. McCormick and Tim Dobbyn)