Petroleum is derived from the Latin word petra, meaning rock or stone, and oleum, meaning oil. It comprises a variety of liquid hydrocarborn compounds made up of different proportions of the elements carbon and hydrogen. Petroleum source rocks are fine grained sedimentary rocks from which it is difficult to extract large quantities of or gas. These rocks are also termed 'reservoir rock'. Well testing has progressed to become one of the most powerful tools for determining the complex reservoir characteristics. Well tests are performed by significantly changing the flow rate of a well. This book provides an approach into the techniques and procedures that are used by the expert engineer to effectively carry out a test under various conditions. The book also covers all the major operational aspects of oil and gas well testing. It uses a structured approach to guide the reader through the various steps that are required to effectively plan and implement a well test operation under just about any circumstances world-wide on-shore or off-shore.