Shares of Occidental Petroleum Corp.          OXY,         +3.95%        rallied 3.6% in afternoon trading Tuesday, enough to pace the S&P 500’s          SPX,         -0.42%        energy sector gainers, after the oil and natural gas company disclosed that Warren Buffett’s Berkshire Hathaway Inc.          BRK.B,         +0.15%        boosted its stake in Occidental to more than 20%. Occidental disclosed in a late-Monday filing that Berkshire Hathaway increased its investment in Occidental by 6.68 million shares, valued at $390.72 million, to 188.37 million shares, or 20.2% of the shares outstanding. At current prices, Berkshire Hathaway’s common stock stake is valued at $11.72 billion. The shares were purchased in a series of transactions from Aug. 4 through Aug. 8, at a weighted average price of $58.4763, according to a MarketWatch analysis of filing data. That price is 6.0% below current levels. The purchase further distances Berkshire Hathaway as Occidental’s largest shareholder, as the second-largest shareholder is Dodge & Cox at 10.75%, according to FactSet data. Occidental’s stock has soared 114.6% year to date, while the SPDR Energy Select Sector ETF          XLE,         +1.76%        has climbed 34.3% and the S&P 500          SPX,         -0.42%        has shed 13.5%.