This article was updated at 3:29 p.m. with additionaldetail

The pool of internal candidates to eventually replace WarrenBuffett as Berkshire Hathaway's chief executive has expanded tofour, the company said in a regulatory filing Monday.

The revered 80-year-old investor has said for several years thatthe Omaha-based company had three internal candidates to replacehim as CEO someday, but has refused to name them.

Berkshire plans to split Buffett's job into three parts — chiefexecutive officer, chairman and several investment managers.

Buffett remains in good health and has no plans to retire, buthe says Berkshire's board regularly discusses succession and knowswho it would pick as CEO if the need arises.

Buffett's assistant Carrie Kizer said he was travelling Mondayand would not be immediately available to comment.

The revelation about a fourth candidate reinforces speculationthat Burlington Northern Santa Fe CEO Matt Rose became a contenderafter Berkshire acquired the railroad last year.

The other Berkshire managers believed to be on the short listare David Sokol, chairman of NetJets and MidAmerican Energy; AjitJain, who runs Berkshire's reinsurance division; Greg Abel,president and CEO of MidAmerican Energy; and Tony Nicely, chiefexecutive of Geico.

Berkshire shareholder Glenn Tongue, who is a managing partner atthe T2Partners investment firm, said he's satisfied with thecompany's succession planning and the details Buffett hasdisclosed. He said naming the CEO candidates could actually becounter-productive because executives who were left off the listmight be discouraged.

"I think he's walked the line on succession planning exactlyappropriately," Tongue said.

Buffett says his primary responsibilities at Berkshire aredeciding how best to invest the company's cash and keeping keymanagers of Berkshire subsidiaries happy. Buffett consults with87-year-old Vice Chairman Charlie Munger on all majordecisions.

But Buffett and Munger employ a remarkably hands-off approach tomanaging Berkshire's roughly 80 subsidiaries. Berkshire'sinsurance, furniture, utility, jewelry, clothing, carpet and othercompanies largely operate independently of Berkshire's 21-personheadquarters.

On the investment side, Buffett has said Berkshire's investmentduties would likely be split among three or more different managerswho would report to the next CEO. Those investment managers will bein charge of Berkshire's stock portfolio and its otherinvestments.

Buffett has said his company's board had a list of severalinternal and external investment managers who could manageBerkshire's investments. Last fall, Buffett hired Todd Combs tomanage $1 billion to $3 billion of Berkshire's $158 billioninvestment portfolio, but no other candidates for the investmentmanager jobs have been named.

Buffett has recommended that his son Howard take over aschairman to ensure Berkshire's culture is preserved, but thatdecision will be made by Berkshire's board. Howard Buffett alreadyserves on the board.