This thesis describes a field study performed on El-Badr oil field located in southern Tunisia. We incorporated petrophysical and reservoir performance data along with well history to better understand and reduce technical uncertainty. We used production analysis to estimate individual well drainage radius, in order to estimate oil in place per well, replicate reservoir properties and estimate reserves under current conditions. We evaluated water origin using water oil ratio diagnostic plots. In conjunction with well tests and layers properties, we evaluated the remaining reserves and reservoir performance potential on layer basis. Suggestions for reservoir management are discussed in detail. We reallocated oil rates within the wells from total measured production. Our approach is pressure based and uses different allocation methods to determine individual well rates on daily basis. Finally, we give recommendations for future activities in reservoir management and development.