We propose a tractable model of asymmetric platform oligopoly in which
users from two distinct groups are subject to within-group and cross-group network
effects and decide which platform to join. We characterize the equilibrium when
platforms manage user access by setting participation fees. We explore the effects of
platform entry, change of incumbent platforms’ quality under free entry, and partial
compatibility on market outcomes. We show how the analysis can be extended to
partial user participation and zero fees for one of the user groups.