In layered reservoirs having hydrodynamically separated, vertically stacked reservoir units it is desirable to design both, production as well as injection for the individual units separately in order to optimize recovery of each unit. Nevertheless especially if some of the units are relatively thin, vertical wells penetrating all units, producing commingled are used in order to minimize development costs. Todays smart completion technologies, e.g. using inflow control valves, provide means to design and hence optimize production from the individual zones. This master thesis assesses the benefits of an optimized reservoir zone production and injection for each separated reservoir unit for such a type of reservoir compared to simple commingled production. The general findings were applied to the Hakim field in Libya. The Hakim field is operated by Zueitina Oil Company. It is located in the Southwest Sirte Basin in the Concession NC74A. The productive horizon in the field is the Facha Member of the Gir formation, which consists predominantly of a dolomite/limestone sequence. Based on petrophysical characteristics the reservoir has been divided into 12 layers. These layers have remarkable variation in thickness, porosity, permeability and other characteristics. Two of the layers are considered to be of non-reservoir quality, hydrodynamically separating the reservoir into 3 individual reservoir zones. Since the start of continuous production in 1985 the field is operated by both commingled production as well as water injection. State of the art reservoir simulation software would be used to investigate the benefits of optimized production and injection for each reservoir unit compared the currently performed simple commingled production from the zones.