Drilling performance of 77 high-temperature production and reinjection wells in the Hengill Area in Iceland was analyzed. The results demonstrate that the perceived high risk of drilling in a proven field is less than commonly thought. No difference was found in the time required to drill holes of 13(3)/8 '' or 9(5)/8 '' production casing but the wider wells delivered 30-40% more steam. The average power output per drilled well amounts to 5.9 MWe but 7.5 per productive well. To predict steam mass flow on the basis of the Injectivity Index one must consider reservoir conditions and enthalpy of the expected inflow into wells. (C) 2013 Elsevier Ltd. All rights reserved.