Bank deposits are usually of a relatively short-term duration while loans made by banks tend to be longer-term – this requires banks to hold reserves to provide liquidity when depositors withdraw their money. Banks, working on the expectation that only a proportion (or 'fraction') of depositors will seek to withdraw funds at the same time, keep only a fraction of their liabilities as reserves. Thus they can experience an unexpected bank run when depositors wish to withdraw more funds than the reserves held by the bank. In that event, the bank experiencing the liquidity shortfall may borrow from other banks in the interbank lending market; or (if there is a general lack of liquidity among the banks) the country's central bank may act as lender of last resort to provide banks with funds to cover this short-term shortfall.