Simulation is widely used as a tool for analyzing business processes but is mostly focused on examining rather abstract steady-state situations. Such analyses are helpful for the initial design of a business process but are less suitable for operational decision making and continuous improvement. Here we describe a simulation system for operational decision support in the context of work ow management. To do this we exploit not only the work ow's design, but also logged data describing the system's observed historic behavior, and information extracted about the current state of the work ow. Making use of actual data capturing the current state and historic information allows our simulations to accurately predict potential near-future behavi...