Editor’s Note: This is the second in a multi-part series examining the fundamentals behind the structural transformation of the U.S. oil market and the downstream logistics challenges that are resulting.

Nearly 150 years after trains first revolutionized the U.S. oil trade, crude is hopping the rails once again as operators, producers and traders try to cash in on the biggest domestic price gap in decades.

Although still relatively small, shipments of oil in rail tankers may have already doubled from a year ago, according to several media reports citing industry ...