Summary Various types of supervisory-control and data-acquisition (SCADA) systems are in use in oil fields around the world, assisting field personnel in maintaining safe and profitable operations. The Upper Zakum field, one of the largest offshore fields, requires a far more extensive SCADA system with higher levels of distribution than generally needed. This paper outlines the environment and extent of the field, emphasizing the need for unmanned operation and the evolution of the Zakum telesystem to meet the special requirements. Specification and predesign phases are shown to be vitally important parts of the project, in both assessing the telesystem's final extent and predicting what the field operators need to control the field. The telesystem implementation is described in detail, including system architecture, operator facilities, hardware and software considerations, and various interfaces with other systems. The problems encountered during the project and their solutions are discussed, and conclusions are drawn for future projects. The need for the highest available level of technology and the likely consequences of compromising this need because of cost considerations are also discussed. Finally, recommendations are proposed for future selection of large-scale SCADA systems.