Comment by duped
My understanding from some of these articles is that oil isn't literally transported in barrels the vast majority of the time, it's in tanker trucks/rail cars/ships moving from source to refinery to retail the whole way. Part of what makes it fun to "buy a barrel of oil" is that you can't go many places and ask for a barrel, you need to bring the thing to put it in (like a tanker truck or rail car).