A resistivity log (run in uncased hole filled with electrically conductive mud) made with a tool that achieves focusing through the use of additional current electrodes above and below a central measure-current electrode. Bucking currents from the additional electrodes serve to confine the measure current to essentially a narrow disc of current flowing outwardly perpendicular to the sonde. Should the survey current tend to flow vertically in the mud column (because of highly resistive beds), currents from the symmetrically positioned bucking electrodes are caused to increase or decrease in order to maintain the horizontal attitude of the survey-current flow.