Web service technologies are expected to foster the creation of networks of specialists which expose their digital services over the internet for the dynamic discovery of services by other organizations. Although the idea of a global Web service directory, which was considered a key enabler of e-commerce in the dot.com era, seems to have failed with the shutdown of the Universal Business Registry in 2006, the vision of an open market for Web services has regained popularity lately in the context of the service-oriented paradigm and Web 2.0 concepts. Given these latest developments, the interesting question is whether there is empirical evidence of an emergingmarket for Web services. Based on a longitudinal study of Web services directories, this paper aims at analyzing the evolving offering and market structure of B2B Web services. The study suggests that commercial Web services which enable companies to out-task discrete, repetitive tasks to specialized service providers continue to be relatively scarce. However, increasing "professionalization' can be observed given the emergence of Web services specialists in the area of compliance, online validation and alerting. In addition, Web services directories are extending their scope beyond service discovery and evolve into either "real' electronic marketplaces or infomediaries.