Warren Buffett's Berkshire Hathaway Inc. may raise its stake in Burlington Northern Santa Fe Corp. to at least 25 percent on speculation that railroads will haul more freight.

Burlington Northern, the second-largest U.S. rail carrier, said in an Aug. 31 filing that Berkshire disclosed the stock- purchase plan by letter last week. The Fort Worth, Texas-based railroad increased sales each quarter since the start of 2003, even as trucking companies were hindered by higher diesel fuel prices and highway congestion.