Radioisotope water tracers were used extensively during a produced-water preflush of the Redwater field hydrocarbon miscible pilot. The results from tracer injections in two zones in the original oil column of the reservoir provide convincing evidence of a preferred flow direction toward the southwest. In addition, they confirm the existence of communication across the shoal margin between foreslope and back reef facies and provide insight into the different flow characteristics inherent to the back reef and shoal margin. Excellent results were obtained with tritiated water (HTO) and cesium (Cs) tracers; cobalt (Co) tracer performance was poor, most likely because the formation retained the tracer. Summaries and discussions of these results, including an assessment of their effects on the pilot, are presented. The paper examines key factors that contribute to a successful tracing program and describes a wire-line tracer injection tool designed specifically for the project. No attempt is made to assess overall pilot performance because this work preceded the miscible flood.