The interaction among firms in the supply chain is necessary for business process execution and relationship success. One phenomenon of great significance to buyer-supplier relationships is opportunism. Opportunism is defined as behavior that is self-interest seeking with guile. It is manifested in behaviors such as stealing, cheating, dishonesty, and withholding information. Opportunism negatively impacts relational exchange tenets such as trust, commitment, cooperation, and satisfaction. Furthermore, perceptions of opportunism negatively affect firm performance. In lieu of the known negative effects of opportunistic behavior on buyer-supplier relationships, why do agents continue to engage in opportunistic tactics with their exchange partners? A comprehensive examination is necessary in order to understand why sourcing professionals engage in acts of opportunism. Understanding why opportunism occurs will reveal how to deter it, and this remains a gap in the literature. Based on theories in economics, marketing channels, supply chain management, decision science, and psychology, a comprehensive model tested a set of factors hypothesized to drive the use of opportunistic tactics. Factors include buyer-supplier relationship-specific factors, environmental factors, individual personality-related factors, and situational factors. Data was collected via internet survey of sourcing professionals from private industry and government agencies. Common to many studies of ethics, respondents made choices …