Reservation-based operating systems provide applications with guaranteed and timely access to system resources. One of their chief benefits is temporal isolation, which prevents the timing mis-behavior of one task from interfering with other tasks. Such a benefit is appealing enough that many systems [2, 8] desire to recursively apply this reservation model to each of their components. This recursive application provides flexible load isolation among applications, users and other high-level resource management entities such as aggregated flows for network bandwith. The hierarchical reservation study can be applied to hierarchical schedulers [5, 6], that support heterogenous scheduling algorithms. We propose and analyze a hierarchical reservation model in the context of fixed-priority scheduling, rate-monotonic and deadline-monotonic, as used in systems such as the Resource Kernel [11]. Detailed schedulability analyses under both deferrable-server and sporadic-server replenishment schemes, including exact completion time tests under hierarchical deadline-monotonic schedulers, are presented. We also derive the least upper scheduling bound for hierarchical rate-monotonic schedulers. Finally, we describe how to apply multi-reserve PCP [4 ], an extension of the Priority Ceiling Protocol for reservation-based systems, to allow tasks to share non-preemptable resources across the hierarchy.