Estimating the average drainage-area pressure ( p av ) of individual wells is a cornerstone to any reservoir-management practice. Yet conventional methods do not always offer reliable solutions to this vexing problem. This study shows that transient flow-afterflow (FAF) testing offers an excellent opportunity to establish p av in a time-lapse mode, when conducted following operational shutdowns. Instrumented wells are natural candidates for FAF testing.Real-time surveillance offers the opportunity to perform rate-transient analysis that results in drainage volume and, consequently, p av . However, gathering quality rate data commensurate with pressure over a long producing period is fraught with uncertainty, which raises questions about the validity of the p av so obtained. In addition, continuous changes in drainage-boundary conditions pose modeling challenges with a given reservoir model. Therefore, the independent estimation of p av cannot be overemphasized. This paper presents a theroretical framework for transient FAF testing and also shows a pragmatic approach to handling pressure/rate data incoherence.