Minimum reserves

The Eurosystem requires credit institutions established in the euro area to hold minimum reserves on accounts with the national central banks. The Eurosystem's minimum reserves system primarily contributes to stabilizing of money market interest rates and to creating (or enlarging) a structural liquidity shortage. The reserve base of an institution is determined in relation to elements of its balance sheet. In the interest of stabilizing interest rates, the Eurosystem's minimum reserve system enables institutions to make use of averaging provisions, i.e. compliance with the reserve requirement is determined on the basis of the institutions' average daily reserve holdings over the maintenance period. Holdings of required reserves are remunerated at the average, over the maintenance period, of the Eurosystem's rate on the main refinancing operations. Reserve holdings exceeding the required minimum reserves shall be remunerated at zero per cent or the deposit facility rate, whichever is lower.

Indicative calendar of reserve maintenance periods
http://www.ecb.int/events/calendar/reserve/html/index.en.html

Data
http://www.ecb.de/mopo/implement/mr/html/index.en.html#data