The Grayburg reservoir of the Foster-South Cowden field has been produced since 1938 and waterflooded since 1962. Production had declined to near abandonment level at the start of this project in 1994. The initial approach to waterflood optimization was conventional. A flow model was constructed from a geological model that was based on logs and cores. Production data was assembled and validated as were the few measured pressures taken early in the field?s history. Production testing of all wells was initiated with new equipment to provide accurate current production data. Pressure transient testing of all wells was initiated to identify workover candidates and to provide accurate current pressures for history matching. History matching pressures and water cuts validated the flow model and the flow model has since guided field operation, subject to the limits imposed by the spacing of the well data which was one reliable well log per 32 acres of reservoir. At this scale compartmentalization of the reservoir was obvious, requiring the use of 3D seismic to define porosity and flow barriers in the area between wells.