This article describes a study which examined the potential for Galileo to serve mass-market users in the presence of a freely available Global Positioning System (GPS) service. The article first looks at a constellation modelling analysis designed to further optimize the performance of an interoperable Galileo. The construction and use of a propagation model of the urban environment is then examined. Finally, the article estimates the likely impact that the urban and indoor performance of Galileo would have on the usefulness and marketability of GNSS, and what impact this might have on the proposed public-private partnership for Galileo. The analysis reveals that Galileo has a slightly better availability over Europe than GPS, but neither system alone can provide reliable visibility of satellites.