The successes which have been obtained with electrical methods of prospecting in detecting metallic ore bodies have led to repeated attempts to use them also in oil prospecting, both in structural work and in locating the oil itself. These attempts have not met with as much success as the application of electrical methods to the location of ore bodies; however, the interest in the possibilities of electrical prospecting as applied in oil work has been aroused again of late, due to the perfection of the resistivity and potential-drop-ratio method in regard to the determination of the depth to geologic bodies.

The object of the writer is to give a summary of the whole field of the resistivity methods, with particular reference to the recent developments. The factors affecting the resistivity of rocks, and methods for the determination of resistivities of rocks and formations are described. Then follows a description of the various surface-potential methods. First, the resistivity methods proper are discussed, with reference to electrode arrangement, apparatus, and methods of interpretation used. Second, the potential-drop-ratio methods are treated, also with regard to the electrode arrangements, apparatus, and methods of interpretation. The opinions of various authors are discussed who have expressed their views about the possibilities of locating oil directly by electrical methods, and exa ples are presented of results which have been obtained thus far with resistivity methods, both in structural prospecting and in attempting to locate the oil directly.