Intisar 103E field is located approximately 260 km south of Benghazi in the Sirte basin, concession 103. The field was discovered in 1968. The objective of this work is to optimize the recovery and to update the 103E LG reservoir simulation model based on a geological study performed by Franlab 2002 and on additional production data obtained since 1996. The model should offer the possibility for a better reservoir management, production monitoring and optimization. Numerical simulation is often the most appropriate tool to evaluate reservoir performance. A third generation multi purpose simulator (SURE) was chosen for this task. As mentioned above, the goal of the thesis is to develop a methodology and based on it a workflow for optimizing oil recovery for this reservoir. The work is based on an already existing geological model and available production, PVT and rock data. Special emphasis was given to the influence and problems that may arise from commingled production such as cross flow between the individual reservoir units. Further, investigating if a communication between the edge aquifers appended to each of the pools exists or not. Some important issues were also addressed in this study. For instance, well spacing and how it is designed to achieve optimal recovery. The requirement for injection wells, (gas and/or water) to increase production and their trajectories was investigated too. Several simulation runs were conducted and the results were analyzed.