A complete system for continuous logging of borehole temperature gradients has been developed and subjected to field tests with prototype equipment. To meet the requirements of this system, a time-domain operator was derived consisting of a smoothing term, a deconvolution term (to compensate for lag due to the thermistor time constant and probe velocity), and a gradient term. When convolved with raw field data, this combined operator will yield directly a high-precision, high-resolution temperature gradient profile.The system was field tested in two partially cased, water-filled boreholes. There was good correlation between gradient logs and thermal resistivity profiles from laboratory measurements on core material, indicating that even in cased wells the gradient log is a good approximation of the thermal resistivity profile. For a lowering rate of 18 m/minute, the gradient profile exhibits a repeatability better than + or -0.5 degrees C/km. Comparison of the gradient profile with a fine-scale geologic log indicates a stratigraphic resolution threshold on the order of 2 m for a 10-20 percent thermal resistivity contrast. For isolated resistivity contrasts of 50-100 percent, the resolution is better than 0.5 m.