ABSTRACT The prominent examples of linear flow behavior in the well test literature relate to linear flow within or to a fracture penetrated by a producing well. The resulting pressure transients generally are exhibited in the early portion of a well test and are followed by infinite-acting radial flow behavior and/or boundary effects. In this paper, the linear flow occurs in the formation, which has a predominantly linear shape. Analysis of interference, drawdown, and build up tests is described in theory and illustrated by practical examples. The necessary equations for the analysis are provided for testing gas, geothermal steam, and oil wells. In elongated linear flow systems, the pressure transient behavior associated with linear flow occurs late in the drawdown or build up test. The type curves provided in this work show that this pressure behavior is readily distinguishable from conventional well tests, particularly in interference tests.