Abstract: A method for measuring formation resistivity uses a tool including a central current electrode and a series of voltage electrodes arranged in pairs on either side of the current electrode. A series of measurements is made using the current electrode with different numbers of pairs of voltage electrodes maintained at a predetermined voltage so as to allow resistivity in the formation to be determined with different depths of investigation. In this manner these measurements are focused and are relatively unaffected by the borehole or by adjacent layers in the formation. The central current electrode is segmented azimuthally into a series of electrodes, and the current flowing out of each azimuthal segment is measured separately. This can yield resistivity images of the formation surrounding the borehole. The azimuthal imaging capability can be used for stratigraphic or lithologic analysis of the formation and to detect fractures in the rock.