Setting aside the fact that the world is not an optimum currency area (not  9  However, network externalities and transactions costs would work against multiple reserve currencies, as they did during bi-metallism and the pound/dollar period under the gold standard.
10  The well-known Triffin (1960) dilemma, which argued that, in order for the global economy to have sufficient liquidity, the United States had to run balance-of-payments deficits; but such deficits could undermine confidence in convertibility.