HDRec (Hot Dry Rock economic) is a cost-benefit analysis program for geothermal projects that combines economic aspects with the technical characteristics of the surface installations and the hydrogeological and thermal properties of the subsurface. Investment and operation costs are evaluated and related to the revenues gained from electricity sales. The program also accounts for discounted cash flows when determining the characteristic financial parameters, as well as the time dependency of operation costs, and the reduction in income ensuing from decreasing reservoir temperatures. It is also possible to factor in the expense incurred for maintenance or refurbishment during production, as well as the cost of dismantling the system when exploitation ends. A simple tax model is also incorporated in the economic calculations. The characteristic financial parameters can be referenced to the start of exploration, or to the beginning and end of commercial energy production. A description is given of the workflow of the HDRec program, followed by an example of its application to a dataset representing conditions in the Upper Rhine Valley of France and Germany. The paper also provides a sensitivity analysis of the influence of the parasitic power demand of pumps and of different subsurface heat exchange areas between boreholes. Finally, a scenario is proposed for optimizing the economic performance of the system using the latest information on the characteristics of the Soultz-sous-Forets reservoir. (c) 2006 CNR. Published by Elsevier Ltd. All rights reserved.