If there is a credible link to a US Gov t definition for the capacity of a tradable barrel of oil then it should be referenced in the main article As the article states there are several definitions for the capacity for a barrel 42 or 55 gallons I highly doubt that the US gov t is or was responsible for defining the capacity of a barrel of crude oil used for commerce or that it is a world wide legal requirement to use a US gov t definition but if there is any such legal requirement then again a reference should be stated in the main article To say that NYMEX has no legal right to define measurement units is a bogus argument What NYMEX has is the right to define or specify units that are pertinent to trade If NYMEX states that oil is to be traded in terms of barrels then it is not illegal for NYMEX to state the capacity of this thing called a barrel in terms of unambiguous STANDARD units or to point to an authoritative source authoritative as far as NYMEX is concerned that defines the capacity of a barrel