It's well known that contango is limited by the full carry, still I believe it can exceed the full cost of carry on rare occurences. How often does that happen ? Now it's also well known that in backwardation there is no limit to the premium the front month can command over deferred months. I don't quite understand this, the premium can not be arbitraged away since the physical can't be borrowed and shorted against future purchase. But why hasn't finance come up with a way to do this, after all borrowing the physical to sell it then paying it back with a future delivery should be feasible ?