Computation of hydrocarbon reservoir volumetrics is offered by 3D numerical integration of the reservoir grids. Values of Original Oil in Place, Original Water in Place, Gross Reservoir Volume, Upscaled net porosity and water saturation, areas, etc. are computed in high detail.
Once GeolOil delivers you reliable estimates of oil and gas reservoir volumes, you can start fluids reservoir simulation studies to estimate a recovery factor and hence the reservoir oil reserves.