The reason for this research originates from the time- and functional dependencies between firms' activities and resources in supply chains. These dependencies cause vulnerability. The principal objective of this research is to conceptualize the construct of vulnerability in firms' inbound and outbound logistics flows. The vulnerability construct of this research consists of two components: disturbance and the negative consequence of disturbance. This research is based upon a two-phase process utilizing sequential triangulation. It is proposed that the vulnerability in the inbound logistics flows from sub-contractors, and the vulnerability in the outbound logistics flows to customers, may be measured and evaluated by four principal dimensions, namely: service level, deviation, consequence and trend. In addition, a model of inbound and outbound vulnerability scenarios in supply chains is introduced for teaching and training purposes, as well as to position and compare the outcome of replication studies of vulnerability in firms' inbound and outbound logistics flows. © MCB UP Limited.