Web services promise to allow businesses to adapt rapidly to changes in the business environment, and the needs of different customers. The rapid introduction of new web services into a dynamic business environment can lead to undesirable interactions that negatively impact service quality and user satisfaction. In previous work, we have shown how to model such interactions between web services as feature interactions, and reason about undesirable side-effects of web service composition. In this paper we present the results of subsequent research on a classification of feature interactions among web services. Such a classification is beneficial as we can then search for ways of detecting and resolving each class of feature interaction in a generic manner. To illustrate the interactions we use a fictitious e-commerce scenario.