Plenty of discourse has been swirling around Berkshire Hathaway's recent investment in energy giant ExxonMobil (NYSE:XOM). For the second quarter in a row, Warren Buffett added a Big Oil name to his portfolio, but both ExxonMobil and Suncor (NYSE:SU) are just pieces to his energy empire. In this segment, we rank the top four energy companies in Berkshire's immense portfolio.  

This segment is from Tuesday's edition of "Digging for Value," in which sector analysts Joel South and Taylor Muckerman discuss energy and materials news with host Alison Southwick. The twice-weekly show can be viewed on Tuesdays and Thursdays. It can also be found on Twitter, along with our extended coverage of the energy and materials sectors @TMFEnergy.

Joel South has no position in any stocks mentioned. Taylor Muckerman has no position in any stocks mentioned. The Motley Fool recommends National Oilwell Varco. The Motley Fool owns shares of National Oilwell Varco. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.