PurposeBased on a survey study of 138 software buyers in Turkey, this study examines conditional indirect effects of requirements uncertainty on supplier opportunism where buyer dependence, a proxy for relation-specific investments, undertakes a mediator role. The authors consider a two-level moderation effect of trust and contract in buyer–supplier relationships throughout the software project lifecycle.Design/methodology/approachA survey-based empirical study was conducted, and conditional process analyses were run using PROCESS macro in SPSS. The present study tests a two-stage moderated mediation model in which competence-based trust with a detailed contract setting moderates the mediational path from requirements uncertainty to buyer dependence.FindingsThe data obtained from the buyer side in the Turkish software industry showed that a relationship in which the buyer is structurally dependent begins at a high level of trust. On the other hand, the authors found that contractual rigidity fosters supplier opportunism ex-post in evolving process of the relationship.Originality/valueThis study contributes to project management literature by testing a two-level moderation effect of governance and the mediator role of buyer dependence in the relationship between requirements uncertainty and supplier opportunism. Moving differently from the previous studies, this study integrates contributions of both economic perspectives, such as resource dependence theory and transaction cost analysis, and relational perspectives into the information processing view.