When the primary oil production stage becomes very week in an oil field, enhanced oil recovery (EOR) methods such as water injection or/and surfactant flooding should be implemented in order to produce the oil remaining in the porous medium. The surfactant flooding aims at lowering the interfacial tensions between the oil and water phases, improving the displacement efficiency. However, different factors have detrimental effect on robustness and performance of surfactant stimulation like as surfactant loss due to adsorption on the reservoir rock which impairs the performance of chemical flooding, consequently renders the process impractical economically. Through this book various factors which have effect on efficiency of chemical stimulation in petroleum reservoirs specially in carbonates are investigated systematically. Such a systematic investigation appears very instructive to choose a proper surfactant for purposes of enhanced oil recovery (EOR) and reservoir stimulation in petroleum industries.