(Reuters) - Warren Buffett's Berkshire Hathaway Inc boosted its ownership stake in Occidental Petroleum Corp to about 23.6% after buying nearly 3.7 million additional shares.
Berkshire disclosed the purchases, which cost about $216 million and occurred on March 23 and 27, in a U.S. Securities and Exchange Commission filing on Monday night.
Buffett's company began buying large quantities of Occidental stock just over one year ago, around when Russia invaded Ukraine, and has spent more than $1 billion on the stock this month.
It now owns about 211.7 million Occidental shares worth $12.6 billion based on the oil company's closing price of $59.65 on Monday.
In August, Berkshire won U.S. Federal Energy Regulatory Commission permission to buy up to 50% of Occidental's common stock.
It also owns $10 billion of Occidental preferred stock with an 8% dividend, plus warrants to buy another $5 billion of common shares at $59.62 each.
Berkshire is Occidental's largest shareholder, and some analysts and investors have speculated that it might eventually buy the Houston-based company.
Buffett, 92, has longed to make another large acquisition for his Omaha, Nebraska-based conglomerate, whose dozens of businesses include Geico car insurance and the BNSF railroad.
Berkshire built a 22.6% stake in BNSF before paying $26.5 billion for the remainder in 2010.