This paper presents a method where fluid flow units are used in reservoir description. We developed the proposed method using core and well-log data from the Endicott field on the North Slope of Alaska. Sedimentary intervals of the cored wells are divided into major zones on the basis of core description information. The major zones are further subdivided into subzones to allow less variation in geologic and petrophysical properties within each subzone and more variation between the subzones. On the basis of the transmissibility, storativity, and net-to-gross-thickness data, the subzones are classified into four distinct fluid flow units by use of the statistical method of cluster analysis. We use a regression relationship established between the core and well-log data in the cored wells to estimate the permeability of the uncored wells, allowing for extension of flow units to these wells. We present stratigraphic cross sections to illustrate areal variations of the petrophysical properties in the Endicott field.