Warren Buffett’s Berkshire Hathaway now owns almost 20% of Burlington Northern after put options it wrote were exercised. Over the past year or so, Buffett has continued to buy up shares in Burlington Northern, the country’s second largest rail company. He has previously said that “railroads have good long-term prospects and are healthier today than in past years,” according to the Associated Press.

CNBC’s Warren Buffett’s Watch, written by Alex Crippen, provides additional detail on the option trade that resulted in Berkshire buying another 3.3 million shares of the railroad.