This paper analyses different operational central bank policies and their impact on the behaviour of the money market interest rate. The model combines profit maximising behaviour by commercial banks with the central bank supplying the liquidity that keeps the market rate on target.It seems that frequent liquidity supplying operations represent an efficient tool to control money market rates. An averaging provision reduces the use of standing facilities and interest rates volatility in all days except for the last day of the maintenance period. Whenever banks have different maintenance horizons both the spikes in volatility and use of standing facilities disappear. The paper also compares two different liquidity supply policies and finds that the level of liquidity necessary to keep the rates on target depends on not only the aggregate but also assets values of individual banks.

The paper analyses the relationship between the liquidity shock variance and the size of the reserve requirement. I calibrated the key parameters of the model for the Eurosystem and found that the standard deviation of the shock is roughly 10% of the average bank's current account holding. Using these parameters and a standard interbank model, I was able to reproduce and explain the dual pattern of EONIA behaviour fairly well. In the early stage of the maintenance period, when the rate typically remains stable, it is the expectations that drive the rate, and the martingale hypothesis should hold while the liquidity effect is low. Toward the end of the maintenance period, it is the market liquidity that determines the interest rate behaviour. JEL Classification: E52, E58, E43

In this paper I analyse the determinants of commercial banks' demand for reserves in the interbank market. I first document the pattern in the Eurosystem, where banks deviate from the required reserves balance at the start of the maintenance period only to meet the requirements closer to the settlement day. Using my model I show that this behaviour can be explained by certain trade-related frictions and costs. Examples include potential extra expenses tied to large transactions or the asymmetry between the cost of borrowing and profits from lending. I also find that borrowing decisions can be largely unaffected by current liquidity, which has important implications for the implementation of central bank monetary policy: in order to influence the level of interest rates, the central bank must focus on controlling market expectations.

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