There are costs in maintaining large currency reserves. Fluctuations in exchange rates result in gains and losses in the value of reserves. In addition, the purchasing power of fiat money decreases constantly due to devaluation through inflation. Therefore, a central bank must continually increase the amount of its reserves to maintain the same power to manage exchange rates. Reserves of foreign currency may provide a small return in interest. However, this may be less than the reduction in purchasing power of that currency over the same period of time due to inflation, effectively resulting in a negative return known as the "quasi-fiscal cost". In addition, large currency reserves could have been invested in higher yielding assets.