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In service-oriented architectures, composite services depend on a set of partner services to perform their tasks. These partner services may become unavailable due to system and/or network faults, leading to an increased error rate for the composite service. In this dissertation, we propose an approach to prevent the occurrence of errors that result from the unavailability of partner services. We introduce an external Web service, FAS (Fault Avoidance Service), to which composite services can register at will. After registration, FAS periodically checks the partner links, detects unavailable partner services, and updates the composite service with available alternatives. Thus, in case of a partner service error, the composite service will have been updated before invoking the partner service. We provide mathematical analysis regarding the error rate and the ratio of false positives with respect to the monitoring frequency of FAS for various partner service availability rates. We obtain empirical results regarding these metrics based on several tests we performed using the Amazon Elastic Compute Cloud. We use these results to evaluate our mathematical analysis. We also introduce an industrial case study for improving the quality of a service-oriented system from the broadcasting and content delivery domain.