Warren Buffett has remained upbeat on the sector as regulatory filings showed that Berkshire Hathaway (BRKA, BRKB) bought more Occidental Petroleum (OXY) shares in June and now owns more than 25% of the company. Chevron CVX (CVX CVX ) is Berkshire Hathway's fifth largest publicly traded stock holding, but Buffett has been trimming it in favor of Occidental. An analysis of Berkshire's second-quarter earnings report shows that another $1.4 billion in Chevron was sold last quarter. A previous piece discussed why Berkshire Hathaway favors Occidental Petroleum.