Geophysical diagnostic techniques are being developed to characterize massive hydraulic fractures. The surface electrical potential technique has been used by Sandia Laboratories in cooperation with industry at several locations in the United States. Comparison of field data to model calculations shows that the electrical potential gradients produced by the direct electrical excitation of the fracture well and fracture fluid can be used to map and characterize massive hydraulic fractures. The direction and asymmetry of the fracture can be determined.