A significant number of well pressure tests are conducted in long, narrow reservoirs with closed and open extreme boundaries. It is desirable not only to appropriately identify these types of systems but also to develop an adequate and practical interpretation technique to determine their parameters and size, when possible. An accurate understanding of how the reservoir produces and the magnitude of producible reserves can lead to competent decisions and adequate reservoir management.So far, studies found for identification and determination of parameters for such systems are conducted by conventional techniques (semilog analysis) and semilog and log-log type-curve matching of pressure versus time. Type-curve matching is basically a trial-and-error process which may provide inaccurate results. Besides, a limitation in the number of type curves plays a negative role.In this paper, a detailed analysis of pressure derivative behavior for a vertical well in linear reservoirs with open and closed extreme boundaries is presented. We studied independently each flow regime, especially the linear flow regime since it is the most characteristic