Warren Buffett's Berkshire Hathaway has added 900,000 more shares of Occidental Petroleum (OXY), for $51.7 million, to its portfolio, according to a filing with the Securities and Exchange Commission, Fox Business reports.

This purchase brings Berkshire's total OXY holdings to 143.2 million shares.

Earlier this month, on May 2 and 3, Berkshire bought 5.9 million shares of OXY, after announcing at its annual meeting during the last weekend of April it had a 14% stake in Occidental.

Berkshire first acquired a preferred stake in OXY in 2019. The investment firm also recently added to its Chevron (CVX) holdings.