Matt Dougherty, managing director at Chicago-based money management firm Advisory Research points out that low natural gas prices have been hurting coal companies lately. And since Berkshire owns a utility, Buffett is probably keenly aware of that fact.
It's also worth noting that despite all the rumors, Berkshire has yet to invest in the sector directly.
"I would be very surprised if Berkshire bought a coal company. This might make sense as a contrarian play, but Buffett has never invested in coal," Dougherty said.