This study deals with the determination of the region within a geothermal reservoir that best provides the volumetric average reservoir pressure. This is performed in order to able to determine the proper location for an observation well through which the volumetric average reservoir pressure could be recorded. In this study a numerical work is carried out for determining the proper location for an observation well to be placed for various configurations of reservoir outer boundary conditions and well configurations. Even though either a single well or two wells are used, the results may be generalized to cases where there are multiple wells in the reservoir by using the production/injection well locations as the region where production/injection occurs. The locations of the wells and boundary conditions have been chosen as to cover many of the possible configurations that could take place in practice. The boundary conditions used in this study are of two types; a sealed outer boundary and a constant pressure outer boundary for mimicking the effects of a recharge source. Wells are considered to be either producer or injector wells where a constant rate production or injection scheme is applied. The effects of faults are also considered in this study where the faults are modeled as a very high permeability medium. The results of this study provide various maps for various boundary and well configurations from which the engineer may be able to determine qualitatively where to place the observation well. This study is original in the sense that to the authors knowledge no such study exists in the literature. This study will be filling the gap.