This article suggests that differences in local political structures and credit protection regimes largely account for Bonny's displacement of Old Calabar as the principal slave port of the Bight of Biafra in the eighteenth century, despite Bonny's reputation for being particularly unhealthy for Europeans. We argue that this displacement occurred in the 1730s, several decades earlier than previously thought. We suggest that this was made possible by the early growth and consolidation of royal authority at Bonny. The use of state authority to enforce credit arrangements in Bonny proved more effective than the mechanisms adopted at its closest rival, Old Calabar, where, in the absence of a centralized political authority similar to the monarchy at Bonny, credit protection before 1807 was based on pawnship.