The purchases were made in multiple transactions and cost about $44 million, Berkshire said in a regulatory filing https://bit.ly/3OqZ2tz. The share purchases come nearly a week after Berkshire bought 9.6 million Occidental shares.
Berkshire, the largest individual shareholder in Occidental, now owns about 153.5 million shares worth about $9.04 billion, based on Occidental's Monday close.
Occidental's share prices are currently up nearly 90% this year, as the company benefited from Berkshire's purchases and an oil price surge following Russia's invasion of Ukraine.
The company also owns options to buy another 83.9 million Occidental shares, which if exercised, would bring its stake to more than 25%.
Berkshire has been on a spending spree this year.
It spent $51.1 billion on equities in the first quarter, including an increased $25.9 billion stake in oil company Chevron Corp.
Berkshire has also this year announced large investments in video game maker Activision Blizzard Inc and computer and printer maker HP Inc, and a planned $11.6 billion takeover of insurance company Alleghany Corp.
(Reporting by Abinaya Vijayaraghavan in Bengaluru; Editing by Sherry Jacob-Phillips)