We analyze the type of market structures that arise in the long-run when quality externalities and asymmetric R&D capabilities exist in the context of a quality-ladder dynamic model. An example of such externalities is a patent release by the leading firm: an improvement of quality of this firm's good aects the quality of the other firms' products. This externality can be thought of as an increase in compatibility in a network. We show that it is possible for this model to generate, in the long-run, multi-modal probability distributions over different market structures from the same parameter values. In some cases, the lagging rm may even become the dominant firm depending on the degree of the externality. This may have implications for the estimation and simulation of this class of models.