By Jonathan Stempel and Sabrina Valle

(Reuters) -A U.S. energy regulator on Friday gave Berkshire Hathaway Inc, the company controlled by billionaire Warren Buffett, permission to buy up to 50% of oil company Occidental Petroleum Corp's common stock.

Occidental's share price soared 9.9%, closing up $6.41 at $71.29, after the Federal Energy Regulatory Commission (FERC) said letting Berkshire add to its 20.2% stake was "consistent with the public interest."

Berkshire had applied to increase its stake on July 11, saying it would not hurt competition, undermine regulatory authority, or boost costs for consumers. FERC regulates the interstate transmission of electricity, natural gas and oil.

The share price of Houston-based Occidental has more than doubled this year, benefiting from rising oil prices following Russia's Feb. 24 invasion of Ukraine. Berkshire began buying Occidental shares four days later.

Buffett's Omaha, Nebraska-based conglomerate also owns $10 billion of Occidental preferred stock, which helped finance the 2019 purchase of Anadarko Petroleum Corp, and has warrants to buy another 83.9 million common shares for $5 billion.

Berkshire also ended June with a $23.7 billion stake in a larger oil company, Chevron Corp.

"Buffett is taking advantage of stock market participants who are foolish about the oil and gas industry and consider it a dead business," said Cole Smead, president of Smead Capital Management Inc in Phoenix, which owns Occidental and Berkshire shares. "Buffett thinks it can make him wealthy."

Berkshire did not immediately respond to a request for comment sent to Buffett's assistant.

Occidental spokesman Eric Moses said the higher ownership limit was "necessary" because the company owned assets subject to FERC regulation. It said the prior limit was 25%.

FERC's authorization does not require Berkshire to buy any Occidental shares.

Some investors and analysts have nonetheless said Berkshire could eventually buy Occidental, diversifying an energy portfolio that includes several utilities, electricity distributors, and renewable power projects including wind.

Buffett completed one of his biggest acquisitions, the $26.5 billion purchase of the BNSF railroad, in 2010 after Berkshire had amassed a 22.6% stake.

TAKEOVER?

Morningstar analyst Greggory Warren said he "liked Occidental more as a wholly-owned subsidiary under the Berkshire umbrella" because it would reduce Occidental's costs to access capital, and reduce exposure to commodity markets volatility.