OMAHA, Neb. — Warren Buffett's Berkshire Hathaway Inc. has reported a 62 percent drop in its 2008 net income because investment and derivative losses of nearly $7.5 billion weighed on the results.

Billionaire Buffett details his worst year leading Berkshire in a shareholder letter issued today.

Berkshire reported $4.99 billion net income, or $3,224 per share, in 2008. That's down from $13.21 billion, or $8,548, in 2007.

Buffett says the Omaha-based company's book value declined 9.6 percent to $70,530 per share in 2008. Berkshire's book value declined only one other time under Buffett, and that was a 6.2 percent decline in 2001.

Buffett says he made at least one major investing mistake last year by buying a large amount of ConocoPhillips stock when oil and gas prices were near their peak.

The famous investor recounted his errors in his annual letter.

Berkshire increased its stake in ConocoPhillips from 17.5 million shares in 2007 to 84.9 million shares at the end of 2008.

Buffett says he did not anticipate last year's dramatic fall in energy prices.

Buffett says he also spent $244 million on stock in two Irish banks that appeared cheap. But since then, he's had to write down the value of those purchases to $27 million.

By The Associated Press