Warren Buffett's Berkshire Hathaway bought 1.62 million shares of BurlingtonNorthern Santa Fe in the past few days, according to a filing late Tuesday with the Securities and Exchange Commission.
The acquisition increases Berkshire's stake to 40.65 million shares about 11.5% of the Fort Worth, Texas-based railroad.
When Berkshire disclosed in April that it had bought 39.03 million shares of BNSF stock, the news sent shares of all major freight railroads higher. Buffett said at the time that he had invested in two other North American railroads, but he wouldn't name them.
A May SEC filing revealed that Berkshire owned 10.5 million shares of Union Pacific and nearly 6.4 million shares of Norfolk Southern .
The latest BNSF purchases took place between Friday and Tuesday, according to Tuesday's filing.
Buffett and Berkshire Vice Chairman Charlie Munger said in May they had decided to invest in railroads because those businesses have a better competitive position today than in past years. Both Buffett and Munger said they were slow to realize that railroads were a good investment because the industry's past performance had prejudiced them.
The filings do not differentiate between investments Berkshire makes, investments any of its more than 60 subsidiaries makes, or investments Buffett himself makes.
Berkshire owns furniture, insurance, jewelry and candy companies, restaurants, natural gas and corporate jet firms and has major investments in such companies as Coca-Cola and Anheuser-Busch .
Berkshire Hathaway's Class A shares gained $690 to close at $112,690 Tuesday before the filing was released. Its Class B shares gained $22 to close at $3,692.
Burlington Northern's shares gained 57 cents to close at $81.25.