The NWS is a major Oil&Gas area in Australia where regional velocity models exist for all the basins located in the province. Using an innovative 3D approach, a model covering the entire NWS has been built and is presented in this paper. The major challenge of the project was to honour as much as possible the resolution of the geological features and to ensure a global consistency of the model in a non-stationary environment at such a wide scale. Another one has been to work with more than 200 surveys and nearly 900 wells as input. The Estimage's 3D approach associated with advanced geostatistical techniques allowed us to build a geologically consistent model with a depth uncertainty far from the wells below +/-100m (at more than 100km from the wells).