Warren Buffett's company says its third-quarter profit tripled as the improving economy and stock market boosted the value of Berkshire Hathaway Inc.'s derivative contracts.

Berkshire said Friday it generated $3.2 billion, or $2,087 per share, in net income. That's up significantly from last year's $1.1 billion, or $682 per share.

Most of the swing in earnings is related to unrealized gains in the value of Berkshire's derivatives, some of which are tied to credit defaults and some of which are tied to equity markets.

Berkshire's insurance companies performed well, but its other operating companies struggled.

Berkshire owns more than 60 subsidiaries and it has major investments in such companies as Coca-Cola Co. and Wells Fargo & Co.