Since the amount of foreign reserves available to defend a weak currency (a currency in low demand) is limited, a currency crisis or devaluation could be the end result. For a currency in very high and rising demand, foreign exchange reserves can theoretically be continuously accumulated, if the intervention is sterilized through open market operations to prevent inflation from rising. On the other hand, this is costly, since the sterilization is usually done by public debt instruments (in some countries Central Banks are not allowed to emit debt by themselves).