Billionaire Warren Buffett's Berkshire Hathaway Inc. acquired another 2.95 million shares in Occidental Petroleum, a regulatory filing showed, bringing his stake in the U.S. oil producer's common stock to nearly 29%.

Berkshire disclosed in a U.S. Securities and Exchange Commission filing on June 17 that it paid about $176 million in three separate purchases of Occidental shares since June 13.

Those acquisitions gave Berkshire about 255.3 million Occidental common shares, an approximately 29% stake worth approximately $15.37 billion on June 17. His purchases this month have totaled 5.5 million shares.

In August 2022, Berkshire won U.S. regulatory approval to buy up to 50% of Occidental, but Buffett has said he has no plans to acquire the Houston-based company.

Analysts and investors have said an acquisition could diversify Berkshire's energy portfolio, which includes several utilities, electricity distributors and renewable power projects.

The Houston, Texas-based company acquired Permian shale oil producer CrownRock in a $12 billion deal last year to boost its presence in the largest U.S. oilfield.

Buffett also owns warrants to purchase another 83.5 million shares of Occidental at $59.62 per share, below Occidental's closing price of $60.20 on June 17.

Occidental shares, which have gained about 1% this year, were marginally up in premarket trading on June 18.