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This paper examines common regulation as cause of interbank contagion. Studies based on the correlation of bank assets and the extent of interbank lending may underestimate the likelihood of contagion because they do not incorporate the fact that banks have a common regulator. In our model, the failure of one bank can undermine the public’s confidence in the competence of the banking regulator, and hence in other banks chartered by the same regulator. Thus depositors may withdraw funds from their, unconnected, banks. The optimal regulatory response to this ‘panic’ behaviour can be to privately exhibit forbearance to the initially failing bank in the hope that it - and hence other vulnerable banks - survives. By contrast, public bailouts are ineffective in preventing panics and must be bolstered by other measures such as increased deposit insurance coverage. Regulatory transparency improves confidence ex ante but impedes regulators’ ability to stem panics ex post. JEL Classification: G21, G28

This paper examines common regulation as cause of interbank contagion. Studies based on the correlation of bank assets and the extent of interbank lending may underestimate the likelihood of contagion because they do not incorporate the fact that banks have a common regulator. In our model, the failure of one bank can undermine the public’s confidence in the competence of the banking regulator, and hence in other banks chartered by the same regulator. Thus depositors may withdraw funds from their, unconnected, banks. The optimal regulatory response to this ‘panic’ behaviour can be to privately exhibit forbearance to the initially failing bank in the hope that it - and hence other vulnerable banks - survives. By contrast, public bailouts are ineffective in preventing panics and must be bolstered by other measures such as increased deposit insurance coverage. Regulatory transparency improves confidence ex ante but impedes regulators’ ability to stem panics ex post.

We analyse a model of financial intermediation in which intermediaries are subject to moral hazard and they do not invest socially optimally, because they ignore the systemic costs of failure and, in the case of banks, because they fail to account for risks which are assumed by the deposit insurance fund. Capital adequacy requirements are designed to minimise the social costs of these effects. We show that banks should always have higher regulatory capital requirements than insurance companies. Contrary to received wisdom, when banks and insurance companies combine to form financial conglomerates we show that it is socially optimal to separate their balance sheets. Moreover, the practice of "regulatory arbitrage", or of transfering assets from one balance sheet to another, is welfare increasing.