Banks as Liquidity Multipliers

Banks hold large amounts of high-quality liquid assets while relying predominantly on deposit funding. The return on these assets is often lower than the cost of deposits. Why do banks engage in such a negative carry trade? Using a novel observation on global games, we build a tractable model where banks manage liquidity risk by adjusting the size of their short-term liabilities and of their liquid reserves consisting of safe, liquid government bonds. Banks are the natural buyers of government bonds because holding these assets enables them to multiply liquidity'': using one unit of bonds to back more than one unit of short-term debt while keeping their liquidity risk unchanged. How much more is measured by the slope of an endogenous iso-risk curve. This liquidity multiplier is key to understand a bank's joint choice of leverage and liquid reserves and how these decisions connect to the pricing of liquid assets. In turn, this provides an explanation of the negative carry puzzle.