The application of pseudo-steady-state and pressure transient response techniques to assist in hydrocarbon volume estimate is presented for a reservoir isolated from its main by a non-sealing fault. The techniques discussed in this paper utilized the pseudo steady state principle to determine the fault boundary behavior dominated flow regime of an oil well which has produced for over eight years in a marginal field of the Niger Delta environment. The material balance technique which utilized accountability of fluid withdrawn/injected and energy conservation principles within the pseudo steady state boundary dominated flow was used alongside with the pressure transient analysis to validate this oil in place number. Seismic attributes was also used to predict the geometry and distribution of the sand based on the conventional seismic interpretation. The seismic attribute analyses clearly show the geometry and spatial distribution of the reservoir sand bodies. Hence, understanding a pseudo steady state dominated regional flow time in a faulted reservoir plays a key role in the management and development of reserves in a marginal field operation.