BILLINGS, Mont. (AP) -- Energy companies behind the oil boom sweeping the Northern Plains increasingly are turning to trains to move their crude across the U.S. The move comes as pipeline plans stall and existing pipelines can't keep up with demand.

Delivering oil by rail to refineries thousands of miles away on the East, West, and Gulf coasts costs more. But it can bring increased profits -- of $10 or more a barrel.

It also means a steady parade of trains carrying the hazardous material rumbling out of North Dakota and Montana and across the country.

Experts and federal regulators say rail transport is less safe than pipelines. That's raised concerns that the proliferation of oil trains could lead to a major derailment and spill.

Companies say they are making track upgrades and other improvements.

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