**FILE** A pair of Burlington Northern Santa Fe engines make their way down the tracks in Midlothian, Texas, in this Jan. 20, 2007 file photo. Warren Buffett's company has bought 10.1 million shares of Burlington Northern Santa Fe Corp. since Thursday, increasing the legendary investor's stake in the nation's No. 2 railroad to nearly 14.8 percent. Berkshire Hathaway Inc. revealed its three latest railroad stock purchases in documents filed with the Securities and Exchange Commission late Monday, Aug. 27, 2007. (AP Photo/Tony Gutierrez, file)