This paper models the relationship between short-term rates and excess reserves in an
interest rate corridor as a logistic function estimated for the Eurosystem. The estimate
helps to identify conditions in which short-term rates become unanchored, that is, they
move away from the policy rates and become more volatile within the interest rate
corridor defined by the interest rates of the central bank's standing facilities. These
conditions are attributed to coordination failures among counterparties at open market
operations under fixed-rate and full-allotment procedures in the context of segmented
markets. A model of the functioning of segmented markets describes how 'un-anchoring'
takes place when counterparties pursue bidding strategies optimal from an individual
perspective but sub-optimal from an aggregate perspective.