A few years after the first oil discovery in 1859, some oil and gas producers in Pennsylvania decided that a barrel of oil should be set at 42 gallons. Forty-two gallons seemed like the most reasonable size for transportation and for floating down the Allegheny River.
A 42 gallon barrel weighed 300 pounds when filled with oil. At that time, men, wagons, horses and boats and barrels moved the area’s oil. Three hundred pounds was about as much weight as a man could handle. Twenty would fit on a typical barge or railroad flatcar. Anything bigger was unmanageable, anything smaller was less profitable.