The result is reported of a TDEM method-based survey for oil exploration conducted in the Yoneyama district, Niigata Prefecture. The survey covered the southern part of the sedimentary basin in the prefecture, known for the poor quality of the seismic prospecting data that had been recorded. The purpose of the TDEM method-assisted survey was to probe the high-resistivity volcanic rock structure and low-resistivity sedimentary layer, and to know their details. The obtained data were subjected to interpretation by use of the 1D inversion method. A 4000m-deep level was subjected to interpretation, 34 data were inputted, and the early model consisted of 20 layers. As the result, it was found that there was a high-resistivity layer ranging from the ground surface down to a depth of approximately 500m, that a low-resistivity layer 2500-3000m in thickness lay thereunder, and that the lowest layer had a high resistivity of approximately 100 Ohm m. By comparing these data with the geological structure, structures were disclosed corresponding to the rock bed depth, Ukawa syncline, Ishiguro anticline, and Yoneyama mountain mass. 3 refs., 10 figs., 1 tab.