Global Ocean Thermal Energy Conversion (OTEC) resources are assessed for the first time with an ocean general circulation model (OGCM). Large-scale OTEC operations are represented with fluid sources and sinks of prescribed strength in global (4 degrees x 4 degrees) MITgcm simulations. Preliminary steady-state (time-asymptotic) results show similarities, but also significant differences with earlier one-dimensional (1-D) studies. It is confirmed that global OTEC resources are likely limited by OTEC flow effects on the stability of the vertical oceanic thermal structure. Such a limit is several times greater in a full three-dimensional context, however, with an estimated maximum annual OTEC net power production of about 30 TW. The significant OTEC flow rates corresponding to maximum net power output would result in a strong boost of the oceanic thermohaline circulation (THC). In contrast to simple 1-D analyses, the present simulations of large-scale OTEC operations also show a persistent cooling of the tropical oceanic mixed-layer. This would be balanced by a warming trend in the higher latitudes, which may practically limit OTEC deployment to smaller flow rates than at maximum net power output. An annual OTEC net power production of about 7 TW, for example, could be achieved with little effect on the oceanic temperature field. (C) 2012 Elsevier Ltd. All rights reserved.