Performance Forecasting is a comprehensive modeling technique used to simulate the existing performance of a complex process, such as a chemical plant, a refinery or other production and distribution networks. Having done this, the impact of a major change can be modeled and calculated upfront; a typical example is the planning of a revamp or a de-bottlenecking project. Assumed gains in extra output of the plant, improved reliability etc. can be confirmed or rejected in an early phase of the project. Modeling the current and future situation of a plant makes it easy to calculate different or alternative scenarios.