In this study, we identify a suite of fluid flow pathways and estimate permeability distribution for The engineered geothermal reservoir at the European enhanced geothermal system test site at Soultz-sous-Forets, France. The work is based on the 2005 hydraulic connectivity experiment between the injection borehole GPK3 and the production boreholes GPK2 and GPK4. We use a massive Monte Carlo approach, together with a geostatistically based assignment of permeability distributions using a stochastic technique, in order to investigate the observed tracer concentration curves. By applying different fitting criteria, 49 single models were selected, providing a good fit to the observation data from a model ensemble of 10,000 realizations. These models are classified in three groups with different flow geometries and permeability distributions, and were analyzed for their Darcy velocities. This approach allows the limits for possible permeability distributions and geometries of the stimulated zones to be quantitatively approximated. (C) 2011 Elsevier Ltd. All rights reserved.