"Mad Money" host Jim Cramer was listening to the show Monday and e-mailed in a two-part question for Buffett. The first part read, "Are we at the golden age of oil and gas, and how is Burlington cashing in on it [train to refinery]." The second part read, "Will [the railroad] switch to nat gas engines on its locomotives?"
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Addressing "the golden age" portion, Buffett said that Bakken oil accounts for 5 percent of shipments at the Berkshire Hathaway-owned railroad.
"We ship 190,000 cars a week. … Coal is 20 percent. So what we've lost in coal we more or less made up in oil. But it's a growth factor, no doubt about it," Buffett said.
Bakken energy is huge and the "job factor is significant," he explained. "We can save hundreds of billions of dollars annually if we get more self-sufficient in oil and gas [in the U.S.]. It's got big, big consequences."
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As for the second part of Cramer's question on converting locomotives to natural gas, Buffett said: "We have a couple locomotives we're experimenting with this year on it. … The railroads are definitely experimenting with converting to natural gas."
He described those experiments as "real enough, so we're spending real money."
"When you get natural gas, you know, at $3.50 and you look where oil is," he continued, "you've got to look at converting any kind of an engine to natural gas."
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—By CNBC's Matthew J. Belvedere; Follow him on Twitter