Every day, as many as 10 oil trains a day leave North Dakota and six to eight travel through Minnesota. They pass through places like Perham, a town of 3,000 in the heart of lakes country. The town may be small, but it is bustling with activity. On one side of the railroad tracks are the shops that draw summer tourists. On the other side are industrial buildings that turn out potato chips, candy, dog food and cheese. Around the clock, semitrailers rumble across the Burlington Northern Santa Fe mainline railroad tracks to and from the factories.