A detailed three-dimensional model of the present well field of the Olkaria geothermal field in Kenya (East Olkaria) has been developed. The model matches reasonably well flow rate and enthalpy data from all existing wells at East Olkaria. The history match shows that the effective permeabilities in the steam zone and the underlying liquid-dominated zone are 7.5 and 4.0 mdarcy, respectively. These values are somewhat higher than those inferred from well test data. The effective fracture porosity in the liquid-dominated zone is estimated to be 2% on the average, with spatial variations of 0.25--5%. The modeling studies suggest that the reservoir system is of rather uniform permeability and that no barriers to fluid flow are necessary to match the data. However, there appears to be a high permeability anomaly below a depth of 1000 m extending north-south through some of the more productive wells (wells 12, 15, 16, and 20). ¿ American Geophysical Union 1986