This paper presents a new, simple, computationally efficient and practical method to accurately calculate effective fracture network permeabilities (EFNPs) for fracture dominated reservoirs. A set of fracture patterns from the outcrops of geothermal reservoirs in southwestern Turkey were chosen and their EFNP values were predicted using the new method; the computed permeabilities are comparable to those obtained with a commercial software package. The proposed method is based on 2-D fracture outcrop data, and is therefore limited to 2-D fracture networks. (C) 2010 Elsevier Ltd. All rights reserved.