We describe here our results using Stoneley waves as an indicator of fracture density in crystalline oceanic basement. During Ocean Drilling Program (ODP) Leg 205, approximately 170 m of oceanic crust was drilled and logged at Site 1253 in order to identify permeable fluid pathways in the downgoing plate of the Costa Rica subduction zone. Logging comprised the Dipole Shear Sonic tool for acoustic full waveform measurements including compressional, shear, and Stoneley waves. We analyzed Stoneley waves, which have velocity and energy content that is inversely correlated to permeability, with a semblance algorithm in order to yield velocity and energy distribution. Our results are in very good agreement with ODP-processed Stoneley velocities in the igneous section of Site 1253, and in addition they yield an energy estimate. In general, the observed velocity and energy loss correlates with zones of borehole breakouts, as predicted by theory. We concentrated on uniform borehole sections where we assume that data are only minimally influenced by geometry and changes in Stoneley wave properties are mainly induced by permeability. By considering fracture abundance obtained from both logging (Formation MicroScanner) and core observations, we found a correlation between increased fracture density and energy losses in these smooth borehole sections. Higher permeability might exist at 468, 492, 500, 508, and 518 meters below seafloor in the lower gabbro. We suggest that fluid flow in the oceanic basement of Site 1253 most likely occurs in these regions.