Agility, speed and flexibility in production networks are required in today's global competition in the flat world. The accuracy of order date delivery promises is a key element in customer satisfaction. Agile production needs a management and evaluation tool for production changes. Discrete event simulation, DES, has mainly been used as a production system analysis tool, to evaluate new production system concepts, layout and control logic. DES can be used for operational planning as well, as shown in the paper. The simulation analysis gives a forecast of the future with given input values, thus production managers have time to react to potential problems and evaluate alternatives. A balance between multiple parallel customer orders and finite resources can be found. The authors are developing a system design evaluation method and also a decision support system for production managers. Two case studies with different approaches are described in the paper.