Rubis is a 3D, 3 phase, multi purpose numerical modeler which sits somewhere between single cell material balance and massive full-field simulation models. It replaces neither, but does much of the work of both. One can build simple numerical models intuitively with no special training. The geometry can be built interactively or can be imported from a geomodeler or another simulator. The unstructured Voronoi grid is built automatically to include finer grid cells close to the wells. The engineer concentrates on the problem, keeps the model updated, running multiple forecasts, reserves and investigation of possible intervention opportunities in a very short time frame, not worrying about the mechanics of 'driving' a complex simulator. Connection is seamless between other KAPPA modules.