In assessing the potential risks of OMTs it should be taken into account that, in principle, the use of monetary policy instruments to maintain price stability entails financial risks for the Eurosystem. This applies not only to OMTs but also to main refinancing operations, to cite just one standard monetary policy instrument as an example.
The Eurosystem uses main refinancing operations to make central bank money available to banks. In principle, these bank loans could also fail, even though the risk of this occurring is slight. Therefore, the European Central Bank’s Governing Council limits these risks, by requiring the provision of  BIS central bankers’ speeches  3  collateral for main refinancing operations.