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PACSR, a probabilistic extension of the real-time process algebra ACSR, is presented. The extension is built upon a novel treatment of the notion of a resource. In ACSR, resources are used to model contention in accessing physical devices. Here, resources are invested with the ability to fail and are associated with a probability of failure. The resulting formalism allows one to perform probabilistic analysis of real-time system specifications in the presence of resource failures. A probabilistic variant of Hennessy-Milner logic with until is presented. The logic features an until operator which is parameterized by both a probabilistic constraint and a regular expression over observable actions. This style of parameterization allows the application of probabilistic constraints to complex execution fragments. A model-checking algorithm for the proposed logic is also given. Finally, PACSR and the logic are illustrated with …