NEW YORK (Bloomberg) — Berkshire Hathaway Inc., with a stock portfolio valued at more than $60 billion, may report its best quarter in at least two years using the metric preferred by the firm's billionaire chairman, Warren Buffett.

About $11 billion in gains in Berkshire's stocks and a recovery of derivative bets tied to equity markets caused book value, a measure of assets minus liabilities, to reverse after two quarters of declines, according to analysts and investors including Glenn Tongue at T2 Partners LLC. Berkshire is set to report second-quarter results tomorrow. "It's going to be a blockbuster," said Tongue, whose New York-based firm's largest holding is Berkshire shares. "It may well be the greatest dollar gain in book value in any quarter in the history of the company. Warren Buffett showed extraordinary discipline in the first quarter when all others were losing their heads."

Buffett, one of the world's most celebrated stock pickers, this year confessed to investing mistakes that hurt returns over the prior 12 months. Berkshire's book value per share, the measure highlighted by Buffett in the first sentence of his annual letter to shareholders, has declined in four of the past five quarters, and 2008 marked only the second time since Buffett took over in 1965 that it dropped for a full year.

In his "owner's manual" for Berkshire shareholders, Buffett says he considers the figure to be an objective substitute for the best measure of the Omaha, Nebraska-based firm's success: a metric he calls intrinsic value.

"Intrinsic value is an estimate rather than a precise figure," Buffett wrote in the manual on Berkshire's website. "The percentage change in book value in any given year is likely to be reasonably close to that year's change in intrinsic value."

The value of shares Berkshire reported holding as of March 31 increased 23 percent in the second quarter. Berkshire is the largest shareholder in American Express Co., whose stock rose 71 percent in the three months ending June 30. Buffett's firm is also the biggest investor in Wells Fargo & Co., which jumped 70 percent and Goldman Sachs Group Inc., which rose 39 percent.