Drilling of the Wairakei geothermal field began in May 1950. The rigs initially used were the small truck-mounted Sullivan 37 and Failing 1500 rigs that could drill to 130 and 460 m depth, respectively. These were augmented in November 1952 with two larger capacity rigs (National T12's) that were rated to about 1500 m. The Continental Emsco GC350 was acquired in 1968 to explore the deep geothermal resource-this rig could drill to about 2500 m depth. By 1965 production drilling was finished at Wairakei, and drilling activity stagnated over the next two decades. Some makeup wells were drilled in the mid-1980s to maintain the steam supply. and at this time investigations began for injecting separated geothermal water into the reservoir. Several test wells were drilled in the late 1980s with the T12 and GC350 rigs, and longer deviated injection wells with a Parker Rig #228 in the early-to-mid-1990s. A few new make-up steam wells were drilled in the late 1990s. The late 1990s and early 2000s saw the disappearance of the venerable Failing 1500s, T12 and GC350. Following a decision in 2005 to optimise the production and injection operations at Wairakei, many new production, exploration and injection wells have been drilled. The main drilling rig for this push has been a Mid Continent U-712-EA which has the capacity to drill to 4500 m. Recent drilling technological upgrades have included the use of a top-drive, aerated drilling, PDC drag bits, larger casing diameters, superior directional drilling technology and downhole video for problem evaluation. As of September 2008, some 180 wells had been drilled in the Wairakei field, totalling over 127,000 m of drilled hole. The outlook for geothermal energy is promising, and there are plans to continue production, injection and monitoring well drilling for years to come at Wairakei. (c) 2008 Elsevier Ltd. All rights reserved.