Warren Buffett’s bid to boost his big stake in Occidental Petroleum even further isn’t expected to serve as a prelude to a full takeover of the resurgent energy company by the widely watched billionaire, at least for now.

In a regulatory filing Friday, the Federal Energy Regulatory Commission said that Mr. Buffett’s Berkshire Hathaway had received permission to buy up to 50% of the driller’s shares. The news stoked speculation that Berkshire could be gearing up to acquire Occidental.