Resource reservation has been recently supported by many real-time operating systems to provide applications with guaranteed and timely access to system resources. Typically, reservations are based on the worstcase requirements, and therefore can inflate resource demands unnecessarily. Many multimedia applications such as MPEG video streams (1) have high worst-case to average-case demand ratio and (2) can tolerate some deadline misses. To support such applications, we propose a "multi-granularity" reservation model. Instead of the classical {C, T, D} model of resource reservation, the multi-granular reserve specification is given by {{C, T, D}, . . . , {C^x, ε^xT_i}, . . . , {C^y, ε^yT_i}} which represents a guarantee of the highest-granularity reserve for C units of resource during every successive periodic interval of T only as long as the resource usage by each of its low-granularity reserves (e.g., C^x units of resource in every recurring time of ε^xT_i, ε^x ∈ Z^+) is maintained. This multi-granular reservation approach delivers higher system utilization than the pessimistic strategy of worst-case reservation and better temporal isolation than other stochastic and heuristic guarantees in the literature. We perform a detailed schedulability analysis of this model using deadline-monotonic scheduling and derive an appropriate admission control test. We also present detailed analyses and simulation results comparing our reservation scheme for MPEG-4 streams with average-case resource reservation, constant bandwidth server (CBS), and (m, k)-firm guarantee.