The Momotombo geothermal field, Nicaragua, has been under commercial production since 1983; presently it has an installed capacity of 77 MWe. A three-dimensional, porous-media numerical model of the system was developed and calibrated using the code iTOUGH2, and was utilized to study the response of the geothermal reservoir under different fluid production and injection scenarios. Satisfactory agreements were obtained between measured and computed discharge enthalpies and flow rates for most of the shallow wells. The model also qualitatively reproduced the pressure drawdowns measured in selected wells. (c) 2007 CNR. Published by Elsevier Ltd. All rights reserved.