April 28 (Bloomberg) -- American Express Co. investors approved a measure making it easier to sell the largest U.S. credit-card lender, with shareholders at the annual meeting speculating that billionaire Warren Buffett's Berkshire Hathaway Inc. is a likely buyer.

The amendment, which reduces the vote required to approve a sale to more than 50 percent from two-thirds, passed today during the company's meeting for shareholders at its New York headquarters. It's also now easier to approve a merger or share exchange, according to the proposal, which passed with about 85 percent of votes in an early tally.

``American Express may be considering eventually to become a private enterprise and become delisted, or become part of Warren Buffett's empire,'' Philip Berman of Berman Asset Management said during the meeting.

American Express Chief Executive Officer Kenneth Chenault told investors he has regular meetings with Buffett, whose Berkshire is the biggest investor in the company. Buffett has said he may spend as much as $60 billion in an acquisition. American Express, which has a market valuation of about $56 billion, has dropped 23 percent in the past year on concern the slowing U.S. economy will hurt consumers' ability to repay debts.

The company rose 12 cents to $47.89 in New York Stock Exchange composite trading at 4:15 p.m.

``I struggle to see why Buffett would be interested in American Express if he couldn't buy it outright,'' Wayne Peters of Sydney-based Peters MacGregor Capital Management said in an interview after the meeting.

`No Plans'

Michael O'Neill, spokesman for American Express, said the company ``has no current plans to effect any of these actions.''

Buffett's Berkshire held 151.6 million shares, or 13 percent of American Express's outstanding stock at yearend, according to Bloomberg data. Jackie Wilson, a spokeswoman for Omaha, Nebraska- based Berkshire Hathaway, didn't immediately return a call.

``To come out of nowhere to do this is highly unusual, I've never seen it in 30 years,'' Berman, based in Rochelle Park, New Jersey, said in an interview. ``Maybe it pays for American Express to be a private company.'' Berman declined to say how many American Express shares he holds.

American Express ranked first by the total value of purchases and cash advances to U.S. cardholders in the first half of 2007, according to the Carpinteria, California-based Nilson Report, a trade publication. JPMorgan Chase & Co. and Bank of America Corp. are ranked second- and third-largest.

To contact the reporter on this story: Hugh Son in New York at hson1@bloomberg.net

Last Updated: April 28, 2008 16:26 EDT