A robotic drilling system for sub-surface drilling of a well bore (110,203) within a reservoir, the system comprising: a surface controller comprising a computer control system that includes: a communications interface; a drilling fluid supply and management system; a cuttings and spent drilling fluids management system; a power management and supply system; a tether management system; and a tender port; a main tether line(103,213); a robotic management tender(104,200) connected to and in communication with the surface controller by the main tether line(103,213); one or more robotic drill tender; one or more robotic drills(107, 113); and one or more intermediate tether lines(105, 108, 112, 205, 208) each connecting the robotic management tender(104,200) to a robotic drill through a robotic drill tender; wherein the surface controller, robotic management tender(104,200), one or more robotic drill tender, and one or more robotic drills(107, 113) are in communication with each other, such that the system provides power and drilling fluid to the robotic drills(107, 113); characterised in that the robotic management tender (104,200) comprises: a communication system for communicating with the surface controller and the one or more robotic drill tenders and the one or more robotic drills (107, 113); a drilling fluid management system for controlling the flow of drilling fluid to the one or more robotic drills (107, 113); a cutting management system for controlling the flow of cuttings out of the well bore; a power management system for controlling power to the one or more robotic drill tenders and one or more robotic drills (107, 113); a sensor system for sensing the position of the robotic management tender (104,200); and a locomotion system (206, 211, 215) for movement of the robotic management tender (104,200) within the well bore. a surface controller comprising a computer control system that includes: a communications interface; a drilling fluid supply and management system; a cuttings and spent drilling fluids management system; a power management and supply system; a tether management system; and a tender port; a communications interface; a drilling fluid supply and management system; a cuttings and spent drilling fluids management system; a power management and supply system; a tether management system; and a tender port; a main tether line(103,213); a robotic management tender(104,200) connected to and in communication with the surface controller by the main tether line(103,213); one or more robotic drill tender; one or more robotic drills(107, 113); and one or more intermediate tether lines(105, 108, 112, 205, 208) each connecting the robotic management tender(104,200) to a robotic drill through a robotic drill tender; wherein the surface controller, robotic management tender(104,200), one or more robotic drill tender, and one or more robotic drills(107, 113) are in communication with each other, such that the system provides power and drilling fluid to the robotic drills(107, 113); a communication system for communicating with the surface controller and the one or more robotic drill tenders and the one or more robotic drills (107, 113); a drilling fluid management system for controlling the flow of drilling fluid to the one or more robotic drills (107, 113); a cutting management system for controlling the flow of cuttings out of the well bore; a power management system for controlling power to the one or more robotic drill tenders and one or more robotic drills (107, 113); a sensor system for sensing the position of the robotic management tender (104,200); and a locomotion system (206, 211, 215) for movement of the robotic management tender (104,200) within the well bore.