The effect of exit rights on cost-based procurement contracts

We analyze optimal procurement contracts when suppliers learn about project costs over time and retain an ex-post right to exit. In the first period, the firm observes a private signal on the likelihood of high costs; in the second, it learns the realized cost type and decides whether to continue or exercise its outside option. We show that when exit opportunities are sufficiently attractive, the optimal mechanism pools all first-period signals and reduces to a cost-plus contract, with payments tied only to realized, verifiable costs. Attempts to elicit cost forecasts ex-ante backfire: firms strategically under-report expectations, triggering exit in high-cost states and generating overruns. This provides a mechanism-based interpretation of cost overruns as failures of incentive design. Finally, we demonstrate that more generous outside options can raise procurement costs and lower firm profits, identifying conditions where limiting exit rights is ex-ante Pareto improving. (JEL D82, D86, H57)