TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractNumerous chemical options are available for addressing excessive water and gas production problems. The chemistry of most of these options is complicated. A petroleum engineer with an average chemistry background has difficulties understanding these to a level that enables him/her to choose and apply a proper option to the problem at hand. In this paper, we provide a brief overview of all chemical water/gas shutoff (WGSO) options available to date. Monomer systems, polymer gels, relative permeability modifying polymers, inorganic gels, plastics etc. are commonly used chemical options. Less common options include viscous flooding, selective plugging with induced mineral precipitation and other miscellaneous grouting materials. Pros and cons of all these options are also discussed. IntroductionThe need for shutting off unwanted fluid production is common to the entire spectrum of well life cycle. Drillers want to plug-off any lost circulation zone, production engineers want to shutoff any unwanted fluid producing zones in order to move to the next zone, and the asset owners want to plug & abandon any depleted wells at the end of the economic life of wells. However, a production engineer's need to control water and gas production ranges from a simple plugging operation to a more sophisticated selective reduction of permeability of an unwanted phase. A successful choice and implementation of any such technique is as demanding as the objective of the job. Therefore a need for a thorough understanding of the options available, their working mechanism, pros and cons are of paramount importance. This work is an attempt to familiarise petroleum engineers with chemical water/gas shutoff (WGSO) technology.