The radius of investigation is still ambiguous and there is uncertainty in radius of investigation calculation. Every changes of pressure in the reservoir will change the radius of investigation. Thus, these variations will make the maximum radius of investigation difficult to define. To analyze this uncertainty, the pressure changes in a reservoir is evaluated by using the Ei-Function equation to plot the pressure profile which is pressure versus distance of the well graph. Furthermore, the pressure profile graph can be used to set a cut off of pressure difference at the end of transient effect that can be defined as maximum radius of investigation. This project required Matlab software for analytical approach and Eclipse Simulator software for numerical approach. The numerical method is used to prove the analytical method. The analytical method will provide the pressure profile which indicate the pressure of reservoir reading further away from the well. Similarly, the numerical method will generate the pressure of reservoir numerically to indicate the same as analytical method. The homogeneous reservoir is used to analyze this ambiguity where the manipulated variable is the flowrate and production time. The preliminary interpretation showed that different flowrate will not affect the radius of investigation while different production time will affect the radius of investigation.