Currently, at 17 per cent, this level is determined by the Central Bank as part of its anti-inflation policy. The fact that these reserves are un-remunerated certainly acts as a tax on the banks which they try to re-coup by increasing the level of the spread.
However, even abstracting from the reserve requirement, the spread between deposit and lending rates can still be considered high. In theory, high spreads can represent the level of oligopolistic power (or the lack of competition) in the banking system as well as an indicator of the level of efficiency of banking operations.