The satellite navigation is an essential technology for implementation of Performance-Based Navigation concept which is one of elements of the future air transportation system. The SBAS, satellite-based augmentation system, is an international standard navigation service with a continental coverage. It provides RNP (required navigation performance) integrity-assured navigation service by augmenting GNSS constellation. We already have four operational SBAS served by the US, Japan, Europe, and India. A possible issue is due to the fact that an SBAS does not broadcast the information on which SBAS should be used by each user in the flight modes of Enroute to NPA (Non Precision Approach). And, the ICAO SBAS SARPS, as well as RTCA WAAS MOPS, does not define any procedure, or satellite selection criteria, to be used by receivers to choose SBAS satellites for use. This means that each user receiver has its own satellite selection scheme if it is tracking multiple SBAS signals; The criteria is actually dependent upon the implementation of each receiver. Additionally, the receivers automatically choose SBAS satellite and apply augmentation information; In general, flight crews have no knowledge on which SBAS is used for their operation. Actually, in Japanese airspace and surrounding regions, recently Indian GAGAN became available in addition to existing MS AS; The GAGAN GS AT-10 captures the whole of Japan within its coverage. In the region, Russian SDCM, Chinese SBAS, and Korean SBAS are additionally planned to be implemented in near future. In such a situation, SBAS satellite selection criteria is an issue because user receivers may track SBAS satellites of different systems simultaneously. Of course, the situation is fully dependent upon the implementation inside receivers. The authors have made an investigation on this issue to identify the characteristics of candidate satellite selection criteria including methods based on elevation angles of broadcasting satellites, the number of available satellties, and computed protection levels. The consideration is based on the actual SBAS messages broadcast from MSAS and GAGAN. Another issue might be the necessity of monitoring the performance of the system operated by ther States. SBAS is an RNP navigation system with integrity assurance likely to be used as a primary means of navigation. The issue is summarized by the question if it is permitted to fly in the airspace of a State dependently upon a primary means of navigation provided by another State. A possible way to relax legal issues is to monitor the performance of the system operated by the other States and, if necessary, warn to users in the airspace in case that the system should not be used for navigation. In summary, the paper describes possible issues at the region where multiple SBAS are available with a real example between Japanese MSAS and Indian GAGAN. The characteristics of candidate satellite selection criteria and performance monitoring of the systems operated by the other States are discussed. Benefits to permit to use primary navigation sources operated by the other States will be concluded.