The Cerro Dragón asset, located in Golfo San Jorge Basin, Argentina, has around 30 producing structures; each one containing from 20 to 50 separate, highly heterogeneous, reservoir horizons, from 6 to 30 feet thick. From 2000 to 2005 oil production grew from 48,000 BOEPD to over 116,000 BOEPD, largely due to optimization and expansion of waterflooding projects: water injection rate was increased from 248,000 BWPD (average of 5 reservoirs accessed per injector-well) to 714,000 BWPD (average of 12 reservoirs accessed per injector-well). In an experimental process started in 2000, injector-well completions were designed and tested in several wells. The experience acquired (successes and problems encountered from 401 completions) was used to improve them as well as to develop new ones. Today, this process continues, testing and enhancing new designs to fulfill the needs of the upcoming waterflooding projects. In addition, it contains information about the procedures and technology used to reduce the completion set up cost and to extend its useful life by solving leakage problems without replacing the completion installation. The objective of this paper is to serve as a reference guide for injector-well completion designs in multilayered fields where a vertical expansion of the waterflooding projects is intended.