Abstract: A method of determining resistivity of an earth formation through a conductive wellbore casing. The resistance of conductors within an armored electrical cable for a wellbore sonde is measured and the sonde is inserted into the wellbore. The sonde has a plurality of electrodes at axially spaced apart locations for electrically contacting the casing. A first electrical current is applied between a first electrode and a surface return electrode and a first current amplitude and phase is measured. A second phase shifted electrical current is applied between a second electrode and the surface return electrode and the second current amplitude and phase is measured. A first voltage amplitude and phase between a first pair of electrodes axially disposed between the first and second electrodes is measured, and a second voltage amplitude and phase between a second pair of electrodes axially disposed between the first and second electrodes is measured.