Service orchestration languages, like the Web Services Business Process Execution Language (BPEL), have been frequently used to provide an implementation platform for model-driven development approaches. As avoidance of vendor lock-in and portability of process definitions are central aims of BPEL, most approaches claim to support a large set of different runtime environments. But, even though today various runtimes for BPEL are available, every runtime implements a different language subset, thus hampering portability. Our idea is to improve this situation by using techniques, the Web Services Interoperability Organization (WS-I) has used to improve services interoperability. We describe a portability profile for BPEL that can detect portability issues in process definitions. Using this profile, we evaluate the portability of BPEL mappings used in several model-driven development approaches.