Warren Buffett’s Berkshire Hathaway Inc. disclosed a $4.5 billion stake in Phillips 66, the Houston-based oil refiner, as the billionaire investor’s company increases its bet on the energy industry.

Berkshire held almost 58 million shares after purchases this week, or more than 10 percent of the total outstanding, according to a regulatory filing issued Friday by Buffett’s Omaha, Nebraska-based company. Phillips 66 closed at $77.23 on Friday in New York.

Buffett and his deputy investment managers, Todd Combs and Ted Weschler, are known for making large, contrary bets on stocks. The latest wager comes amid a slump in crude prices, driven by concerns that a supply glut will persist.

“Berkshire’s made a clear statement about how they view the oil business,” said Cliff Gallant, an analyst at Nomura Holdings Inc. “They seem to be taking the long view that demand for fuel is going to come back.”

Concern over China’s growth roiled global financial markets earlier this week and created a buying opportunity for Berkshire. Phillips 66 shares fell below $70 on Monday amid a broad sell-off before rebounding sharply later in the week.

Still, Berkshire may have been accumulating the stake for some time, given the scale of the holding, said Gallant. The filing discloses the prices Berkshire paid for only a fraction of its stake.

Earlier this month, Berkshire didn’t disclose an investment in Phillips 66 at the end of the second quarter. At the time, Buffett’s firm also said it had omitted some data that was reported confidentially to regulators. The Securities and Exchange Commission sometimes allows companies to withhold information from the public to limit copycat investing while a firm is building or cutting a position.

Buffett requested confidential treatment in 2011 filings, as he spent more than $10 billion amassing a stake in International Business Machines Corp. He did the same while building a holding in Exxon Mobil Corp. in 2013.

The most-recent figure Berkshire had given for a Phillips 66 investment was a stake of 7.5 million shares at the end of March.

Buffett’s company formerly held more stock in the refiner. It used most of those shares to buy a business from Phillips 66 last year.

The Phillips 66 holding is relatively small for Berkshire’s stock portfolio. Buffett’s company has stakes in Wells Fargo & Co. and Kraft Heinz Co. valued at more than $20 billion apiece. It is the top shareholder in Coca-Cola Co., IBM and American Express Co.