The main objectives of this research are to estimate the oil reserves and set a development plan for Hakim Field in Libya, using three methods for calculating OOIP which are Volumetric (Monte Carlo), Decline curve analysis (DCA), Material Balance Equation, and establish the optimum development plan for Hakim field. Results showed that the OOIP of Hakim Field,  calculated by volumetric method done through Monte Carlo tool given 90.2 MM STBO for Proven Reserves (1P) , 115.5 MM STBO for Probable reserves (2P) and 147.0 MM STBO for Possible reserves (3P). While OOIP estimated by Decline curve analysis given 82.4MM STBO for Proven Reserves (1P) , 102.8MM STBO for Probable reserves (2P) and 114.9MM STBO for Possible reserves (3P), and 112.18 MM STBO for Probable reserves (2P) by Material Balance. In addition, 14 prediction scenarios have been applied on the Material Balance Model to establish the optimum Field development Plan, results showed that from simulation model the optimal scenario is 8 Producing Wells, 4 Water Injector Wells and 8000 BWPD.