Buffett appeared on CNBC Monday after releasing his letter to Berkshire Hathaway shareholders Saturday. Buffett owns BNSF railroad and a manufacturer of tank cars.
Buffett says the crude oil from the Bakken oil field in North Dakota and Montana and the Eagle Ford oil field in south Texas has proven more volatile than anticipated.
That volatility may have contributed to several fiery derailments in the past year, including one in Lac-Megantic, Quebec, last summer that killed 47 people.
New safety rules being drafted by federal regulators may not be completed until later this year.