User-generated online reviews are an important decision aid for consumers affecting purchase prob-abilities and sales figures. However, little is known about factors influencing the review generation process. Thus, this paper empirically examines the impact of cross-organizational spillover effects on user-generated online service reviews. Specifically, we study how the overall perception of consumers towards a service provider expressed in online reviews is affected by upstream service providers in interdependent service chains (ISCs). Based on the Treatment-By-Association (TBA) phenomenon, we design a research model to study both the existence and evolvement of cross-organizational spillover effects in online reviews of ISCs. Utilizing every airline and airport review posted over 13 years on www.AirlineQuality.com, we show that both positive and negative spillover effects exist: Increased (decreased) overall ratings of an upstream service node are associated with increased (decreased) ratings of the directly following service node in the ISC. In addition, we show that this is not true for more distantly arranged service nodes. We contribute to the IS research stream of online reviews by shedding light on spillover effects and by providing evidence for the proposed TBA. Furthermore, suggestions how practitioners could manage and utilize spillover effects to improve their customer experience are provided.