A new inversion method for P wave anisotropy <Wu and Lees, 1999a> has been applied to high-precision, microseismic traveltime data collected at Coso geothermal region, California. Direction-dependent P wave velocity and thus its perturbation, are represented by a symmetric positive definite matrix A instead of a scalar. The resulting anisotropy distribution is used to estimate variations in crack density, stress distribution and permeability within the producing geothermal field. A circular dome-like structure is observed at the southwestern part of the geothermal region southwest of Sugarloaf Mountain. Using a linear stress-bulk modulus relationship, deviatoric stress is estimated to be 3--6 MPa at geothermal production depths (1--2 km), assuming all the anisotropy is related to stress. The stress field is compressional NNE-SSW and dilational WNW-ESE, coinciding with a previous, independent study using earthquake focal mechanisms. Following a theory on flat, elliptic cracks, residual crack density estimated from P anisotropy is ~0.0078 assuming crack aspect ratios≫1:60 and is ~0.041 when crack aspect ratios are close to 1:60. Residual crack orientation distribution is related to velocity anisotropy. On the basis of anisotropic part of crack density distribution function, the anisotropic part of permeability distribution may be calculated by a statistical approach via simple parallel fluid flow along cracks. ¿ 1999 American Geophysical Union