When it comes to Warren Buffett and Berkshire Hathway (BRK.A – Get Report), the numbers are often mind-boggling: $70 billion net worth; shares that sell for hundreds of thousands of dollars each; dozens of portfolio companies and more.

Mr. Buffet is known for his long-term bets when companies are facing potential undervaluation.

Cliff Gallant, an analyst at Nomura Holdings Inc.

Concern over China’s growth roiled global financial markets earlier this week and created a buying opportunity for Berkshire. The filing discloses the prices Berkshire paid for only a fraction of its stake.

Earlier in August, Berkshire said it had omitted some information in public filings, but it had been conveyed to regulators confidentially.

The new investment is up sharply from Berkshire’s last disclosure.

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.

The SEC sometimes lets Omaha, Nebraska-based Berkshire do this so Buffett can quietly buy a large amount of stock, without worrying about investors piggybacking on the famed investor’s apparent stamp of approval.

Berkshire as soon as held a big stake in the Houston-based firm, however shed nearly two-thirds of it in February 2014 when it swapped $1.35 billion of shares for a chemical compounds enterprise that it folded into its Lubrizol unit.