Under the current competitive market environment, buyers and sellers strive to develop and maintain close business relationships to achieve greater competitive advantages. However, this relationship arrangement often fails at a very high rate due to the existence of opportunism. Research scholars have empirically investigated this issue. Yet, to date, opportunism has not been studied explicitly. Empirical attentions have been devoted to define sets of governance mechanisms that deter opportunism rather than trying to understand what the root causes are. Moreover, the causes and effects of this phenomenon have not been systematically integrated. Previous empirical studies also produced inconsistent results. In addition, there is relatively limited empirical attention given to studying this issue from an international exchange context, especially in utilising information obtained from both sides of the exporter-importer relationships. In response to these literature gaps, the present study focuses on exploring the drivers and outcomes of opportunism in international buyer-seller relationships . Drawing on the transaction costs analysis theory and a key aspect of the international theory, a comprehensive conceptual model integrating antecedents and consequences of opportunism in export-import relationships is proposed. A set of research hypotheses that illustrates the link between drivers, opportunism and outcomes is formulated. The hypotheses are tested by using data from mail surveys of Thai exporting manufacturers and their UK importing distributors. The data are analysed through structural equation modelling. The results suggest that psychic distance and performance ambiguity have a positive effect on opportunism, whereas transaction-specific investments have a negative effect. Moreover, opportunism significantly increases transaction costs and therefore reduces the performance of the relationship. However, there is no significant link found between environmental uncertainty and opportunism. The research findings are discussed in accordance with the results from previous empirical studies. The theoretical, managerial and public policy implications are also presented, along with the limitations and possible fruitful avenues for future research.