Abstract: This work intends to present an analytical and a simulation model for an online reservation system and examine its performance associated with its bottlenecks. The modeling and evaluation of reservation systems should be carried out through analytical models, whenever these models are available. However, it is known that in general, such models have approximations that do not consider several details of the real world. Because the multiprocessing system in consideration uses database queries (and also uses preemption resume priority) and has a certain degree of complexity, our approach uses an approximate analytical model that is validated by a discrete-event simulation model (and vice-versa). Both models are supported by data obtained from measurements of a real-world system. Once validated, the model can be analyzed for other input data and distributions through simulation Ver menos