Abstract Marketing and Strategy studies have treated relational governance as a critical factor of business-to-business (B2B) performance. Extant studies offer contrasting views on whether formal or social control is a better control mechanism, with little known about their interaction effect. In this study, the authors aim to investigate the interaction effect of these two control mechanisms by dividing a B2B contract (formal control) into two provisions (transactional and relational) and to examine the specific interaction effect of social control on each provision. The authors also seek to investigate the moderating effects of environmental dynamism, prior ties, and buyer lock-in. The measure of B2B performance reflects relational quality and financial outcome. The results show significantly different interactions between each provision of the contract and social control depending on the level of environmental dynamism and buyer lock-in, and suggest that the environmental condition of the transactions is reflective of managers' optimal control mechanisms.