Service-Orientation (SO) is a design and integration paradigm that is based on the notion of well defined, loosely coupled services. Within SO, services are viewed as computational elements that expose functionalities in a platformindependent manner and can be described, published, discovered, and consumed across language, platform, and organizational borders. SO principles emphasize composability, by which a set of services can be composed to achieve the desired functionality. Service orchestration is the dominate approach to service compositions. A key issue in implementing service orchestrations is their efficient concurrent execution. This paper focuses on the scalability challenges of simultaneously executing many long-running service orchestration instances. We present a novel approach for implementing service orchestrations called BUST (Break-Up State Transition) that significantly improves processing rate and scalability. Categories and Subject Descriptors C.2.4 [Computer-Co...