Production decline under all its aspects, sometimes controllable, but more and more inconsistent with the growing demands of the natural gas market, has imposed a new approach on mature gas reservoirs which Romania owns, namely, their rehabilitation. During exploitation, after recording a considerable production history and implicitly a appreciable depletion, it is necessary the evaluation of maintaining or changing the exploitation strategy. The approaches in this sense must be from the perspective of improving the value of mature gas fields. Throughout the exploitation of a gas reservoir generally there are distinquished several stages, such as gradually increase of gas flow rates due to increasing gas wells introduced into production, maintaining of a quasi-constant production, a accentuated decline of gas flow rates of the reservoir respectively a attenuated decline of gas flow rates of the reservoir. The first three stages are quite short reported to the whole exploitation process of the reservoir. The production decline appears sooner or later depending on the manifestation form of the reservoir energy. For the accuracy of the baseline which is to be established, can be taken in discussion, as reference intervals, those periods from the production history, in which the points dispersion is minimal, and flow rates respectively the production are comparable with the current ones. Taking into consideration the decline values obtained from decline curve analysis characteristically to every exploitation stage, we consider that to define the baseline production afferent to the next stage, it is optimal to accept the specific decline of the latest exploitation period. It can be noted that throughout production history, although the exploitation of the gas reservoir was intensified, due to accessing new reserve volumes, the decline tendency is to maintain at a limited interval. This behavior indicates the fact that also in conditions of intensifying the exploitation in the future, the decline will maintain a value sensitively close to the values from the latest periods, in which rehabilitation was applied.