As we noted previously, something unexpected has been going on in overnight funding markets: ever since March 20, the Effective Fed Funds rate has been trading above the IOER. This is not supposed to happen.

As a reminder, ever since the financial crisis, in order to push the effective fed funds rate above zero at a time of trillions in excess reserves, the Fed was compelled to create a corridor system for the fed funds rate which was bound on the bottom and top by two specific rates controlled by the Federal Reserve: the "floor" for the corridor was the overnight reverse repurchase rate (ON-RRP) which usually coincides with the lower bound of the fed funds rate, while on top, the effective fed funds rate is bound by the rate the Fed pays on Excess Reserves (IOER), which served as the corridor "ceiling."