Qualified personnel are the key to keeping a plant running safely and efficiently. Process trainers and OTS\' are tools that allow operators to practice on virtual plants. The core of this tool will be the dynamic model (either the one developed for preconstruction studies, if following the lifecycle approach; or a built on purpose model for the OTS), which will be connected to custom made interfaces for operators and instructors. A process trainer (or early OTS) fits into the gap between a full featured OTS system (dynamic model connected to an emulated DCS) and a standalone dynamic model. A process trainer can be developed as soon as the dynamic simulation model is ready and once it has been enhanced with the control strategy. It has a self made DCS ‘look and feel’ instead of an emulated DCS. This intermediate option can even sound attractive for small new investments and smaller existing plants and, in comparison with an OTS can have lower costs.