Berkshire Hathaway announces a $5 billion investment in oil giant Occidental Petroleum

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Warren Buffett complained in his annual letter to shareholders, which was released less than a week ago, that he could "find little that excites us" in the equity markets.

However, according to a new SEC filing from Friday night, someone at Berkshire Hathaway, either Buffett himself or his portfolio managers, is very excited about Occidental Petroleum.

Berkshire Hathaway owns 91.2 million common shares of the oil giant as of Friday. At tonight's close of $56.15, they're worth $5.1 billion. The stock is up 18% today and 45 percent this week.

It has risen sharply in tandem with the price of oil, which has risen to around $115 per barrel in the aftermath of Russia's invasion of Ukraine.

Berkshire Hathaway was buying as Occidental was rallying.

More than 61 million shares are now in its portfolio, with prices ranging from $47.07 to $56.45.

The remaining 29 million shares were acquired this year on or before Tuesday. (In its most recent 13F filing, Berkshire reported holding no OXY shares as of December 31.)

Berkshire did not respond to CNBC's request for comment on Friday night.

We don't know when or how much Berkshire paid for those 29 million shares because it hadn't yet reached the 10% ownership level that requires new purchases to be disclosed within a day of being made.

Berkshire owns only about 9% of Occidental's common stock. However, it also has warrants to purchase an additional 83.9 million shares at a price of $59.62 per share.

Even though the warrants have not been exercised, they must be counted for the purposes of the SEC filing trigger, putting Berkshire's stake at more than 17 percent.

Berkshire received the warrants as part of a deal that included Occidental receiving a $10 billion loan in 2019 to help it buy Anadarko for $38 billion.

The loan, which takes the form of Berkshire's purchase of preferred stock, requires Occidental to pay an annual dividend of 8%. This equates to $200 million per quarter.

Buffett told CNBC at the time that it was a long-term bet that oil prices would rise.

In the second half of 2019, Berkshire acquired a relatively small stake of just under 19 million shares. It was worth around $780 million at the end of that year.

In the short term, Buffett's bet on oil prices did not fare well when they crashed in early 2020 as a result of the COVID-19 pandemic.

To save money, Occidental made first and second quarter loan payments to Berkshire in the form of stock to Berkshire. (It then resumed cash payments.)

Berkshire received 17.3 million shares in the first quarter and 11.6 million in the second.

However, its 13F filings did not show any OXY stock as of June 30 and September 30 in 2020, indicating that it had sold both the 19 million shares it purchased and the nearly 29 million shares it received as dividend payments amid the oil market turmoil.

Now that oil prices have recovered, it has re-entered Berkshire's portfolio in a big way.