The TDS technique is a practical, easy, and powerful tool for well test interpretation. It uses characteristic features and points found on the pressure derivative versus time plot, so that reservoir parameters can be easily calculated by using several analytic expressions. Most calculations can be verified more than once and applied to systems where the conventional straight-line method has no applications. This book deals with well tests run in elongated systems, partially completed/penetrated wells, multirate tests, hydraulically fractured wells, interference tests, and naturally fractured reservoirs. This technique is used in all commercial well-testing software. Its use is the panacea for well test interpretation and can also be extended to rate-transient analysis, although not shown here.