Recently Ouenes et al.1–4 used extensively simulated annealing to generate permeability and porosity fields. In this paper, the Simulated Annealing Method (SAM) is applied to a gas storage reservoir. The permeability field predicted in four geological layers preserves the spatial distribution and honors the actual measured data from the field. These known data at the wells lead to isotropic and anisotropic variograms which were matched by SAM. In this approach, contrasting the usual conditional simulation, no interpolation technique is used to smooth data at unknown locations. The generated field is compared to a kriged field by using a 3D advanced gas reservoir simulator. When using permeability fields generated by SAM, gas and water pressure data obtained through simulation become very close to observed field pressure data. On the other hand, the pressure obtained with the kriged field clearly shows that the smooth representation introduced by the kriging is not realistic, and the heterogeneities which affect considerably the flow behavior are not well described.