Sandvik Tamrock Corp has developed an underground rock flow simulation tool OPTIMINE which is a direct simulation tool for matching suitable technology in rock material flow for underground mine layouts and production requirements. The tool gives the possibility of determining intersections, limitations and critical points in the layout and working procedures at an early stage of a new mine/mining area planning process. The tool combines the supplier machine knowledge with operational know-how and mine environment. It can be used for identifying the effect of an individual incident such as the effect of one additional turn in a continuous loading cycle to the daily capacity. This paper discusses the way the OPTIMINE simulation tool operates, the benefits and restrictions, and reviews how it simulates some example cases and how the mines benefit from the tool in maximising the performance and optimising the mobile fleet, scheduling work and fine-tuning the layout.