Warren Buffett's buying spree of Occidental Petroleum is showing no signs of stopping, and Wall Street firm TD Cowen said investors should follow suit. Berkshire Hathaway purchased an additional 3.7 million Occidental shares for $216 million on Monday and last Thursday, boosting the conglomerate's stake in the Houston-based energy producer to 23.5%, a new regulatory filing showed. The legendary investor has been adding to his already-large stake this month — 7.9 million shares across March 13-15 as well as 5.8 million shares from March 3-7 — as oil prices weakened and concern grew about the health of U.S. regional banks. OXY 1Y mountain Occidental TD Cowen upgraded Occidental to outperform from market perform on Tuesday following the news. On top of Occidental's strong fundamentals, the Wall Street firm said the "captive buying support from Berkshire Hathaway" is a catalyst for the stock. "Berkshire buying shows little evidence of slowing," TD Cowen said. "We see a superior risk-reward balance of superior exposure to crude pricing, capital structure shifts, captive buying support from Berkshire Hathaway, a favorable free cash yield, well productivity and a differentiated catalyst rich profile in a world of relatively homogeneity across E & Ps." In August, Berkshire received regulatory approval to purchase as much as a 50% stake. Berkshire also 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 . Occidental is now among Berkshire's top 10 holdings. The stock has pulled back about 5% this year following a banner 2022, when it was the best performer in the S & P 500, more than doubling in price. The stock was up about 2% premarket Tuesday.