Cloud-based Software-as-a-Service (SaaS) providers want to grow into the space of business process outsourcing (BPO). BPO refers to the systematic and controlled delegation of many steps of a company's business process. BPO is a new and important extension to SaaS, as it allows the provider to add more value in the online application services and as it enables the outsourcer to obtain more cost efficiency. BPO results in decentralized federated workflows. To describe these workflows, companies often use business process modeling languages. Currently, Business Process Modeling Notation (BPMN) is one of the best-known standards. It is crucial to ascertain that the modeled workflow is executed as intended. Errors that happen during execution of a federated workflow can come with huge costs. Validating the model is limited to syntactical checks and there is little support for validating the execution at design time. In this paper a method is presented to validate the correct execution of BPMN 2.0 Collaborations. The methods in this research use concepts from virtual time previously described for Web Services Choreography Description Language (WS-CDL). To validate the results of this research, the Eclipse BPMN modeler was extended with an implementation of the validation method.