In general, consumer preferences depend on the context of a decision situation. This paper highlights the context-dependence of substitution behavior in out-of-stock (OOS) situations and provides evidence for the relevance of promotion as essential driver of customers' OOS reactions. We demonstrate both theoretically and empirically how OOS-induced preference shifts can be explained and predicted using context and phantom theory. In a series of experiments, we show that consumers substitute in accordance to a negative similarity effect, which is reduced for stock-outs of promoted low-involvement FCMGs. If a similar substitute is offered at a reduced price, the effect is enforced. For dissimilar substitutes, we show the contrary. The empirical findings further suggest an augmented probability of purchase postponement and a significant smaller chance of brand switching for stock-outs of promotional products. Furthermore, our study emphasizes outlet switching as a so far uninvestigated OOS reaction and discusses implications for retailers and manufacturers.