(Bloomberg) – Berkshire Hathaway Inc. has bought nearly $590 million of Occidental Petroleum Corp. stock this week, after the Texas oil company agreed to buy private Permian producer CrownRock LP in one of the biggest energy deals of the year.

The purchases were made in five tranches after the deal was announced on Dec. 11, according to a regulatory filing published late Wednesday. Berkshire has been buying Occidental stock steadily over the last three years and is now the company’s largest shareholder with a stake of just over 27%.

Berkshire first invested in Occidental in 2019 to finance its $55 billion purchase of Anadarko Petroleum. Occidental Chief Executive Officer Vicki Hollub didn’t need Buffett’s help to fund the $10.8 billion CrownRock acquisition but Berkshire’s purchases this week will likely be seen as a sign of support for the deal.