We investigate the requirements of Scientific Workflows in context of the Business Process Execution Language for Web Services (BPEL4WS/ BPEL. The complexity, unpredictability and inter-dependency of the components in a scientific workflow often demand flexibility in a workflowlanguage in order to support; 1) exception handling, 2) recovery from uncertain situations, 3) user interactions to facilitate interactive steering and monitoring, 4) dynamism to adapt to the changing environment, 5) compensation handling to roll back, and 6) support for dynamic selection of services. We illustrate these requirements with examples taken from a real scientific workflow; the e-HTPX project for high throughput protein crystallography. In this paper, we discuss the application of BPEL, which is widely regarded as the de-facto standard for orchestrating Web Services for Business Workflows with a large set of features to support complex requirements. These features, along with other standard tools, can be adapted to fulfill the requirements of Scientific Workflows.