The body has now taken a stake in Texas-based NRG Energy as energy prices continue to rise, Bloomberg reports.
Berkshire has also reduced its holding in Anheuser-Busch, the maker of Budweiser beer, following the firm's announcement last month that it could be bought out for $52 billion.
Speaking to the news agency, Frank Betz at Carret Zane Capital Management commented: "The changes in the investment vehicle's portfolio were detailed in a regulatory filing submitted by Berkshire for the second quarter.
"It would be logical for him to increase his utility and energy holdings and NRG would fit in nicely."
I would suspect he's looking at this move that we've seen in energy and he's thinking assets are worth a whole lot more than what the market is currently valuing them at,'' added Calyon analyst Gordon Howald.
Mr Buffett, 77, is thought to be the world's richest man.