The key challenge of gas fuel based fueling stations, such as those for CNG, is to provide a time efficient and safe fill-up for such vehicles. First, the fill-up process is simulated based on a self-consistent thermodynamic model and a dynamic model of the process. Then, the fill-up process is formulated as a minimum time optimal control problem with the aim to minimize the fill-up time while satisfying all safety constraints. The simulation and optimization predictions lead to fill-up strategies that can improve current practices.