Bank Run
A bank run is a situation in which a large number of depositors simultaneously withdraw their funds from a bank because they fear that the bank may become insolvent or illiquid. Because banks hold only a fraction of their deposits as liquid reserves and invest the remainder in longer-term, less liquid assets, a bank cannot satisfy a sudden surge of withdrawals, and a run can force a bank to fail even if its assets are fundamentally sound.
Definition
A bank run occurs when depositors collectively lose confidence in a bank and rush to convert their deposits into cash. The essential characteristic is that the fear is self-fulfilling: because the bank does not hold enough liquid assets to repay all deposits on demand, the belief that the bank may fail can cause the behaviour that makes failure occur.
Bank runs arise from the fundamental mismatch between the liquidity of a bank's liabilities (deposits, which are payable on demand) and the illiquidity of its assets (loans and investments, which cannot be quickly liquidated without loss). This mismatch is inherent to the business of banking and is the source of both its usefulness—maturity transformation—and its vulnerability.
Causes
Bank runs can be triggered by a variety of events. A loss of confidence arising from rumours or adverse news about a bank's solvency may prompt withdrawals. Deterioration in asset quality, such as a rise in loan defaults, may raise doubts about a bank's capital. Contagion occurs when difficulties at one institution spread to others, as depositors infer that similar problems may exist elsewhere. Macroeconomic shocks—a sharp economic downturn, a financial market crash, or a currency crisis—can undermine confidence in the banking system as a whole.
Coordinated runs and the role of expectations
Economic analysis distinguishes between runs triggered by fundamentals—that is, by genuine news about the bank's solvency—and runs driven purely by expectations. In a self-fulfilling run, all depositors rationally choose to withdraw because they expect others to do so, even though the bank would be solvent if everyone remained calm. This multiplicity of equilibria—a good equilibrium in which deposits are stable and a bad equilibrium in which the bank fails—is a central insight of the theory of bank runs.
The potential for self-fulfilling runs, combined with any underlying weakness, makes banking intrinsically fragile. The characteristic of a bank run as a coordination failure is precisely why institutional safeguards such as deposit insurance are effective.
Historical examples
Banking panics have recurred throughout financial history. The Panic of 1907 in the United States saw a series of runs on trusts and banks, prompting the creation of the Federal Reserve System. The Great Depression of the 1930s witnessed thousands of bank failures in the United States, and widespread runs contributed to the destruction of money and credit. The Argentine crisis of 2001 saw depositors effectively locked out of their accounts for a period. The global financial crisis of 2007–2008 produced runs on financial institutions, some of them in the "shadow banking" system rather than at traditional banks—a modern manifestation of the classic phenomenon. More recently, rapid digital withdrawals have shown that runs can occur faster than in the past.
The problem of contagion
A single bank run can spread to other institutions through several channels. Depositors at other banks, seeing the run, may withdraw out of caution, even if they have no specific information about their own bank. Banks that rely on interbank lending may find that funding dries up as lenders become wary. Asset price declines, forced by fire sales of securities, may impair the balance sheets of other institutions. This contagion can transform an individual institution's difficulty into a system-wide crisis.
Prevention and mitigation
A range of institutional arrangements has been developed to prevent bank runs or to limit their damage.
Deposit insurance guarantees that depositors will be repaid up to a specified limit even if the bank fails, removing the incentive to run for insured depositors. Many countries established deposit insurance schemes following the experience of the Great Depression.
Lender of last resort facilities allow a central bank to provide liquidity to solvent but temporarily illiquid banks, stemming a panic. This function was articulated by Walter Bagehot, who argued that central banks should lend freely against good collateral at a penalty rate.
Regulation and supervision impose capital requirements, liquidity requirements, and restrictions on risk-taking, reducing the probability of insolvency and building buffers to absorb losses.
Resolution regimes provide mechanisms for orderly failure of a bank without systemic disruption, including powers to seize the institution, replace management, and impose losses on shareholders and creditors.
Suspension of convertibility and capital controls have historically been used to halt runs by temporarily preventing depositors from withdrawing.
Each of these measures involves trade-offs. Deposit insurance can create moral hazard by encouraging banks to take excessive risks; lender of last resort facilities can do likewise. The design of an effective financial safety net must balance the goal of preventing panics against the need to preserve market discipline.
Theoretical contributions
The study of bank runs was transformed by the work of Douglas Diamond and Philip Dybvig, whose 1983 model formalised the demand-deposit contract and demonstrated the existence of self-fulfilling run equilibria. Diamond and Dybvig received the Nobel Memorial Prize in Economic Sciences in 2022 for this work, which provided a formal foundation for deposit insurance and other policy responses.