Abstract The classical approach to constructing reservoir models is to start with a fine-scale geological model that is densely populated with petrophysical properties. Then scaling-up techniques allow us to integrate this detailed information on a coarser grid and to obtain a reservoir model with fewer grid cells, which can be input in a fluid flow simulator. Geostatistical modeling techniques are widely used to build the geological models before scaling-up. These methods provide possible images of the area under investigation that honor the well data and have the same variability computed from the original data. At an appraisal phase, when few data are available or when data obtained from the wells are insufficient to describe the heterogeneities and the petrophysical behavior of the field, additional constraints are needed to obtain a more realistic geological model. For example, seismic data or stratigraphie models can provide average reser-voir information with an excellent areal coverage, but with a poor vertical resolution. New advances in modeling techniques allow integration of this type of additional external information in order to constrain the simulations. In particular, two-dimensional or three-dimensional seismic derived information grids or sand-shale ratio maps coming from stratigraphie models can be used as external drifts to compute the geological image of the reservoir at the fine scale. Examples illustrate the use of these new tools, their impact on the final reservoir model, and their sensitivity to some key parameters.