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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper is a case study of the redevelopment of a highly complex and heterogeneous reservoir located in the folded belt of Neuquén basin, Argentina. The objective is to describe the integrated reservoir study that was performed; as a consequence, an aggressive drilling campaign was implemented which derived in a boost in production with no substantial interference among wells.The field was in a mature stage as it came into production in 1984 by primary recovery and oil rate was declining steadily.Cerro Fortunoso field represents a challenge for optimising the depletion strategy because of its non conventional qualities such as the presence of an under-saturated oil in coexistence with an extensive CO 2 gas cap, the heavy oil located in a highly heterogeneous fluvial reservoir with poor petrophysical conditions and flanks dipping more than 60 degrees. Besides good data acquisition for seismic is hindered by surface volcanic rocks and complex geology.Field operation is intricate because it is placed in a natural reserve; as a result, drilling and production activities are more expensive in order to comply with environmental regulations.As the reserve to production ratio was exceptionally high compared to other fields in the area, it was suggested that production could be increased but the challenge was how to accomplish this objective in a supposedly fully developed reservoir where the low productivity of the wells had a profound impact on economics.The multidisciplinary team concluded that both the geological and engineering features contributed to a low recovery factor which could be improved by infill drilling. New technology was used to drill 9 vertical and 16 deviated wells in only two years. The results were so spectacular that it not only arrested decline but also established a new peak of production.The conclusions show that many fields that are thought to be fully developed, still have a lot of new oil to be produced.Reservoir management plays a major role by improving final recovery and project economics.