Performance predictions are presented for the East Olkaria geothermal field, using a three-dimensional well-by-well model calibrated against 6.5 years of production history. Various reservior development schemes are investigated to study the effects of different well spacing on well deliverabilities, power production of 45 and 105 MWe (megawatts electric), and the effects of injection on well performance and reservoir depletion. It is shown that the present well density at Olkaria (20 wells/km2) is too high; recommended well density for future wells is 11 wells/km2 (300-m well spacing). The present production area at East Olkaria (2 km2) is capable of 45 MWe power production for a 30-year period, but 105 MWe power production requires a well field area of about 9.5 km2, which may not exist. Injection can help sustain steam flow rates from wells, thus reducing the need for new development wells. ¿ American Geophysical Union 1986