OBAGI is an onshore oil field located on OML58, 85 km north-west of Port-Harcourt, Nigeria. It is composed of 26 stacked reservoir levels with an estimated total OOIP of 1.2 Gbbls. It was discovered in 1964 and has been producing since 1966 through 123 wells and 257 completions. 21 layers have been developed. With a global recovery to-date of 50% and an average producing water-cut of 75%, OBAGI can be considered as a mature oil field. Current activities are driven by two main objectives:to sustain short term production level, andto identify potential remaining resources for additional developments Appropriate monitoring and global static/dynamic review are the key factors to achieve these objectives. The short term objective is to maintain production by optimizing the injection capacity. Difficulties to model reservoir performance have resulted in implementation of an intensive monitoring program. This is to limit water production and to maintain/increase water injection capacity. For the long term, it is believed that potential resources not accessible with current wells could effectively double the remaining reserves. For this purpose, complementary developments have to be proposed to target clearly identified attic oil or by-passed regions. A pragmatic approach was adopted based on 2G model review, material balance study and fluid contact updates (with regular saturation survey campaigns) to identify additional reserves potential. The progress of the study is presented for one of the layers of the field. Introduction OBAGI is an oil field located onshore Nigeria (Figure 1) and discovered in 1964. The OOIP has been estimated to 1.2 Gbbls, split in 26 stacked reservoir levels (Figure 2). Oil production started in 1966 and the maximum of 70,000 bopd was reached in 1983. Both oil and gas productions are currently valorised thanks to Obite Gas Plant start-up in 1999 (also located on OML58). Therefore, although Obagi is mainly an oil field, 5 gas caps are also considered for future production. All produced water is reinjected into the field to minimise environmental impact and support the reservoir pressure.