According to a regulatory filing released on Tuesday evening, Warren Buffett’s Berkshire Hathaway increased its already substantial stake in Occidental Petroleum during recent trading sessions.

The conglomerate, based in Omaha, purchased nearly 5.8 million shares of the oil company in several separate trades on Friday, Monday, and Tuesday, paying prices ranging from $59.8 to $61.9 per share.

This latest purchase, which totaled more than $350 million, was the first time the “Oracle of Omaha” had increased his bet since September. Berkshire now holds 200.2 million shares of Occidental, valued at $12.2 billion based on Tuesday’s closing price of $60.85.

Occidental, now among Berkshire’s top 10 holdings, has seen its stock decline by approximately 3% this year after a spectacular 2022. Last year, the energy company was the best-performing stock, more than doubling in value.

During an interview with CNBC’s Brian Sullivan on Monday, Occidental CEO Vicki Hollub revealed that she recently met with the 92-year-old investor Warren Buffett. They discussed the oil and gas industry, as well as the technology involved in it.

In August, Berkshire received regulatory approval to acquire up to 50% of Houston-based Occidental, sparking speculation that it may eventually buy the entire company.

In addition to its stake in Occidental, Berkshire also owns $10 billion worth of Occidental preferred stock and holds warrants to purchase another 83.9 million common shares for $5 billion, or $59.62 each. These warrants were acquired as part of a 2019 deal that helped finance Occidental’s acquisition of Anadarko.