The Omaha, Nebraska-based firm purchased 58 million shares valued at $4.5 billion, Bloomberg reported.
At the end of the second quarter, Berkshire didn’t disclose an investment in Phillips 66, and it appeared that the billionaire investor had chosen to sell all of his nearly 7.5 million shares in the energy company.
However, reports now show that Buffett and his deputy investment managers, Todd Combs and Ted Weschler, had likely been growing their stake in the company for some time and requested confidential treatment.
Buffett is known for requesting confidential treatment from the Securities and Exchange Commission, which permits companies to withhold information from the public in order to limit others from copying their investments while they build their portfolio.
He made the same move while building up his portfolio in Irving, Texas-based Exxon Mobil Corp. (NYSE: XOM) in 2013.
Phillips 66 is the largest Houston-based public company by revenue, according to HBJ research. The company reported revenue of $164 billion for 2014. Refiners like Phillips 66 have been benefiting from access to cheaper crude, unlike some of its energy peers.
Berkshire Hathaway’s U.S. stock portfolio was worth $107.2 billion as of June 30,the International Business Times reports.