Warren Buffett’s latest energy field play is already making him money.

Buffett’s Berkshire Hathaway reported late Friday that it had bought an 10.8 percent stake in Phillips 66 worth $4.48 billion.

On Monday, in the first day of trading after the news broke, Phillips shares rose 2.4 percent, to $79.07. That added roughly $105 million to Berkshire’s market capitalization.

Berkshire was able to accumulate the nearly 11 percent stake in private because Berkshire has an SEC exception to the 5 percent disclosure rule.