It must be a bear market because even billionaire Warren Buffett's Berkshire Hathaway Inc. has slumped almost 20 percent since December.

The decline exceeds the drop of the Standard & Poor's 500 Index and marks the worst first half for the Omaha, Neb.-based investment and holding company since 1990. Price competition has driven down revenue at Berkshire's insurance units, which account for about half of its income.

Berkshire is "close to getting more fairly priced," said Charles Hamilton, a Nashville, Tenn.-based analyst at FTN Midwest Securities Corp. "I wouldn't say it presents a buying opportunity right now."

After reporting record 2007 earnings of $13.2 billion, the 77-year-old Buffett told shareholders in February that profit margins from insurance would drop.

"That party is over," Buffett wrote in his annual letter to shareholders in February. "It is a certainty that insurance-industry profit margins, including ours, will fall significantly in 2008."

Berkshire also has been hurt by the declines of Wells Fargo & Co., American Express Co. and U.S. Bancorp, three of the company's 10 biggest equity holdings, at the end of March. Wells Fargo, Berkshire's second-largest holding, dropped 18 percent in the second quarter, while American Express and U.S. Bancorp slipped 14 percent.

Berkshire declined $1,435 to close Wednesday at $118,665 in New York Stock Exchange composite trading, and is down 20 percent since its all-time closing high of $149,200 on Dec. 10. That exceeds the 17 percent slide of the S&P 500 in the same period. Berkshire spokeswoman Jackie Wilson didn't respond to a request for comment.