The incorporation of multiple constellations into satellite based augmentation systems (SBAS) may lead to cases where there are more corrected satellites in view than a receiver has tracking channels. This paper addresses two related topics: identifying the most important satellites to track in order to provide availability; and identifying a recommended number of channels. Previously, the SBAS minimum operational performance standards (MOPS) specified a minimum number of channels required for the user receiver. It is possible to obtain significantly worse availability with this minimum number than with the all-in-view solution when employing a poor satellite selection algorithm. Alternatively, it is possible to achieve high availability with fewer than the minimum number of channels and a very good selection algorithm. This paper describes example selection methods that achieve high availability. It further describes a method to specify performance instead of a minimum hardware channel capacity. This form of specification allows for greater flexibility in receiver design. Manufacturers would be allowed to choose between more channels combined with a simpler algorithm versus fewer channels and a more sophisticated algorithm.