Buyers in supply chain exhibits risk avoidance preference in making inventory ordering decision under supply uncertainty. In supply chain with stringent service level requirement, out-of-stock aversion is an important risk avoidance preference of decision makers in making inventory orders. This research explores the individual-level behavioural determinants of out-of-stock aversion in supply chain facing risk of supply disruption. The aim is to enhance understanding of buyer’s behavioural preference for out-of-stock aversion by proposing a conceptual model based on the risk construct theory and the framework of risky decision making. The conceptual model presented here formulates several propositions related to overordering driven by out-of-stock aversion preference. It draws upon extensive literature on behavioural inventory ordering decisions under supply uncertainty and individual risky decision-making to provide a comprehensive understanding of this behavioural preference among the purchasing personnels. The proposed model presents how a buyer’s risk preference influences stockout avoidance overordering. Furthermore, by incorporating the behavioural view of supply disruption risk, the model offers a comprehensive perspective on understanding the behavioural preference of out-of-stock aversion. Findings suggested that individual propensity to risk aversion and perceived supply disruption risk are the key behavioural factors that drive the psychological process behind out-of-stock aversion. The proposed model lacks empirical testing and thus the developed prepositions remain open for validation. This paper lays the groundwork for future empirical research on behavioural perspective of risk driven inventory ordering under supply risks, particularly through field studies.