This paper uses the staggering timing of branching and interstate banking deregulation as a natural experiment to explore the effect of agency cost on the use of bank loan commitments. A simple inventory-based model shows that lower agency cost allows a bank to issue more loan commitments because lower agency cost alleviates the difficulty of liquidity management associated with loan commitments. Our empirical analysis confirms the model’s testable implication: Commercial banks issue more loan commitments after interstate banking deregulation, which lowers agency costs through expanded internal capital markets across states. However, the effect of branching deregulation is weak or non-existent. Considering the role of bank loan commitments, this result not only shows how banking deregulation affects bank balance sheets but also suggests one route through which interstate banking affects the real economy.