The design of Galileo has been conceived so as to facilitate its possible joint use with GPS thus contributing to a favorable multi-GNSS environment. Evaluating the performances of such multi-GNSS combination is crucial for end users to assess the quality of obtainable PVT and the easiness of interoperability of the two systems. In this paper, we evaluate the GPS/Galileo integration performances in terms of estimated precision in position determination and in terms of availability of the service. Results obtained from real data are presented and show that there is an improvement of both these criteria when the two systems are jointly used.