The amount of crude oil U.S. freight railroads hauled last year more than tripled as shale oil production surged in North Dakota and other locations.
The Association of American Railroads trade group said Thursday that U.S. freight railroads hauled 233,811 carloads of crude oil in 2012. That's up from 65,751 carloads the previous year.
Crude oil shipments still represent less than 1 percent of all the carloads railroads haul, but it has been growing significantly in recent years. Each railroad tank car holds about 700 barrels of crude oil.
The railroads have been an attractive option for oil producers because pipelines haven't been able to keep up with production, and railroads offer the ability to ship crude to different destinations.