Shares of Occidental Petroleum ( OXY ) edged higher Tuesday as Warren Buffett’s Berkshire Hathaway ( BRK.A , BRK.B ) bought up even more of the stock, boosting its stake in the energy firm to almost 29%.

Berkshire Hathaway purchased shares every trading day from June 5 to June 17, increasing its ownership by 7.3 million shares, Securities and Exchange Commission (SEC) filings show. The prices paid ranged from $59.58 to $60.43 each.

Berkshire’s Stake Could Pass 40%, But Buffett Says He’s Not Looking To Take Control

With the latest buy, Berkshire has about 255.3 million shares in Occidental Petroleum, bringing Berkshire’s stake to 28.8%. Occidental Petroleum is Berkshire’s sixth-largest holding.

Berkshire also has warrants to buy 83.9 million more Occidental Petroleum shares at $59.62 apiece, and owns 84,897 shares of preferred stock . A full redemption could bring Berkshire’s ownership above 40%, though Buffett has previously said he wouldn’t take control of the company.

Buffett reportedly said in a CNBC interview that he began investing in the company after he read the transcript of one of its earnings reports and said “this is exactly what I would be doing.”

Shares of Occidental Petroleum finished 1.8% higher at $61.26 Tuesday. The stock has gained about 2.6% since the start of the year.