Fluid-mediated interaction between catalyst particles alone is shown to yield several interesting and significant phenomena in a catalytic reactor that have been generally attributed in the past to direct interaction between particles. Thus, collaborative interaction between particles and the fluid may enhance or abate steady-state multiplicity, and reverse stability behavior. From the simple setting of a population of particles in a well-mixed CSTR, it is shown that the catalyst phase in a catalytic reactor is susceptible to very fine pattern formation in the face of steady-state multiplicity in single particles, which negates the usual assumption that particles exposed to a given fluid have identical states. In a reactor such variability in behavior must be accompanied by a corresponding variability in conversion and selectivity (in multireaction systems) and may have strong implications for reactor control strategies.