Warren Buffett's Berkshire Hathaway bought more shares of Occidental Petroleum on each of the last six trading days, boosting its stake in the Houston-based oil and gas producer to 24.4%, according to regulatory filings. The Omaha, Nebraska-based conglomerate purchased a total of of 5.6 million shares for $327.2 million over the past six sessions at an average price of $58 a share. Berkshire now owns 217.3 million shares with a market value of nearly $12.7 billion. Shares of Occidental rose nearly 2% in premarket trading Friday. The stock is down about 7.5% this year, after more than doubling in 2022. The company once known for being founded by legendary oilman Armand Hammer was the best-performing name in the S & P 500 last year. For his part, Buffett has made it clear that he won't take full control of the oil company. There had been speculation of a takeover after Berkshire received regulatory approval to purchase as much as a 50% stake. "There's speculation about us buying control; we're not going to buy control," Buffett said at Berkshire's annual shareholder meeting earlier this month. "We wouldn't know what to do with it." The 92-year-old investor told shareholders that he could be interested in buying more shares, and he's content with the warrants he owns. "We may or may not own more in the future but we certainly have warrants on what we got on the original deal on a very substantial amount of stock around $59 a share, and warrants last a long time, and I'm glad we have them." Berkshire owns $10 billion of Occidental preferred stock, and has warrants to buy another 83.9 million common shares for $5 billion, or $59.62 each. The warrants were obtained as part of the company's 2019 deal that helped finance Occidental's purchase of Anadarko Petroleum . A full redemption of the preferred equity could lift Berkshire's ownership of Occidental above 40%, Wells Fargo estimated. — CNBC's Alex Crippen contributed reporting.