This book is a reference book that appeared and became standard text and aims to provide student and teachers with a coherent account of the basic physics of reservoir engineering. The book has been most successfully achieved without any prior knowledge of reservoir engineering. The material is dealt with in a concise unifield and applied manner, and only the simplest and most straightforward mathematical techniques are used. The book is concise that will continue to be an invaluable teaching aid for years to come. This book served as a very deep and efficient reminder on issues that has been studies in field of upstream in petroleum economics and management course. The book outlines the techniques required for the basic analysis of reservoirs prior to simulation. It reviews rock and fluid properties, reservoir statics, determination of original oil and gas in place by volumetric and material balances, evaluation of drive mechanisms, fluid flow in porous media, aquifer influx, well testing, fluid distribution and displacement, and decline-curve analysis.