The emerging paradigm of service-oriented computing requires novel techniques for various service-related tasks. Along with automated support for service discovery, selection, negotiation, and composition, support for automated service contracting and enactment is crucial for any large scale service environment, where large numbers of clients and service providers interact. Many problems in this area involve reasoning, and a number of logic-based methods to handle these problems have emerged in the field of Semantic Web Services. In this paper, we build upon our previous work where we used Concurrent Transaction Logic (CTR) to model and reason about service contracts. We significantly extend the modeling power of the previous work by allowing iterative processes in the specification of service contracts, and we extend the proof theory of CTR to enable reasoning about such contracts. With this extension, our logic-based approach is capable of modeling general services represented using languages such as WS-BPEL.