HO Scale Tank Cars

One of the most prolific car types you will find moving within a freight train today is the tank car. This versatile piece of rolling stock has long been used to handle liquid or liquefied products, usually some type of chemical or petroleum-based commodity. Its use has increased over the years diversified to also include food-based products and ethanol.However, this was not always the case and in many ways the tank car is a "specialty" freight car, meaning it was originally created to haul a specific commodity. While the perception changed somewhat in recent times, the industry has often been quite stubborn about accepting new technologies, or any change at all for that matter. So, when new oil companies began appearing after reserves were discovered in the 1860s railroads were, not surprisingly, hostile to developing a new type of car to haul the commodity. 

Source: American-Rails.com