The capacity of a car to carry cargo is determined by number of wheels on car. We are talking oil here not automobiles or truck containers. Oil is about(?) as heavy as water. Less connections at a dock to load and unload the Tank-train may be an advantage as can be having equipment no one else can take and use for something else. Disadvantages are special docks, waiting for the oil to flow through the long train, and needing a bigger rip-track when things go wrong.