Warren Buffett's company said in a regulatory filing Monday that it bought another 83,466 shares to give it roughly 79.6 million shares of Phillips 66 stock.
The latest purchases worth roughly $6.5 million were made after Berkshire bought 414,065 Phillips 66 shares last week.
Buffett first started buying Phillips 66 stock in 2012. Berkshire traded about $1.4 billion of its Phillips 66 stock for one of the refiner's additive businesses in 2013.
Then it resumed buying stock in the Houston-based company when prices fell to attractive levels. Berkshire paid an average of $78.29 on its most-recent purchases.
Besides investments, Berkshire owns about 90 subsidiaries in a variety of industries, including insurance, utilities, railroads, and manufacturing.