Most literature on standard selection focuses on compatibility standards for single products or large but single systems that are developing, such as the internet or a telecommunications network. In this study, we focus on systems that connect multiple existing subsystems and new subsystems to form a new complex system. We hypothesize that in these systems, the composition of the networks of actors that are supporting the different competing standards and the flexibility of these standards plays an important role in establishing dominance. Also, we hypothesize that both variables reinforce each other. We test these hypotheses using data that comes from a database that we have created for this study and we find support for these hypotheses.