Abstract: Cost aware service aggregation is described; for example, two or more web services may be connected to form an aggregate service in a way which minimizes computational costs and/or costs of network resources between the services. In an embodiment a service has a two or more contracts expressed using process-algebra which capture data representations and protocols of the web service. In an embodiment, a static analysis engine identifies combinations of contracts which are compatible according to the process-algebra. In an example, the identified combinations of contracts are ranked by cost to select an optimal combination. In other examples, network environment conditions are taken into account and dynamic adjustments made to the aggregation. In more examples, mappings of the data representations to other data representations are considered and appropriate proxy services are automatically used to implement these mappings if required.