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STORY: Warren Buffett said he purchased nearly 800,000 more shares of Occidental Petroleum, snapping up the stock for the second time in less than a week.

It gives his Berkshire Hathaway a more than 16% stake in the Texas-based oil company and pushed its shares up more than 6.5% Tuesday morning.

Berkshire said in a regulatory filing that the latest purchase cost about $44 million.

This after Berkshire said last week that it bought more than $500 million worth of Occidental, on top of a $336 million share purchase last month and $7 billion in purchases earlier this year.

Berkshire, the largest individual shareholder in Occidental, now owns about $9 billion worth of the stock, based on the price at Monday's close.

Occidental's stock is up nearly 90% this year, as the company benefited from Berkshire's purchases and a surge in the price of oil.

Buffett has been on a spending spree this year, with an eye on the energy sector, increasing his stake in Chevron, as well, that's worth almost $26 billion.

Berkshire has also announced large investments in video game maker Activision Blizzard, PC and printer maker HP, and a planned takeover of insurance company Alleghany Corp.