An apparatus for evaluating an earth formation penetrated by a borehole comprising: a two terminal resistivity sensor on a pad , wherein (a) the pad is configured to be proximate to a wall of the borehole ; (b) one of the two terminals of the resistivity sensor comprises at least one current electrode , the at least one current electrode configured to convey a current into the earth formation; (c) a pair of horizontally separated return electrodes horizontally displaced from the at least one current electrode ; and (d) a processor configured to determine a horizontal resistivity property of the earth formation from the current in the at least one current electrode and a voltage between the at least one current electrode and the pair of return electrodes ; characterised in that the apparatus further comprises a pair of vertically separated additional return electrodes vertically separated from the at least one current electrode ; and wherein the processor determines from a current in the at least one current electrode, and a voltage between the at least one current electrode and the pair of return electrodes, and a voltage between the at least one current electrode and the pair of additional return electrodes a vertical resistivity of the earth formation ; wherein the apparatus is configured such that when the measurements are being made with the vertically separated additional return electrodes , the horizontally separated return electrodes are open circuited, and when the measurements are being made with the horizontally separated return electrodes , the vertically separated additional return electrodes are open circuited. a two terminal resistivity sensor on a pad , wherein (a) the pad is configured to be proximate to a wall of the borehole ; (b) one of the two terminals of the resistivity sensor comprises at least one current electrode , the at least one current electrode configured to convey a current into the earth formation; (c) a pair of horizontally separated return electrodes horizontally displaced from the at least one current electrode ; and (d) a processor configured to determine a horizontal resistivity property of the earth formation from the current in the at least one current electrode and a voltage between the at least one current electrode and the pair of return electrodes ; (a) the pad is configured to be proximate to a wall of the borehole ; (b) one of the two terminals of the resistivity sensor comprises at least one current electrode , the at least one current electrode configured to convey a current into the earth formation; (c) a pair of horizontally separated return electrodes horizontally displaced from the at least one current electrode ; and (d) a processor configured to determine a horizontal resistivity property of the earth formation from the current in the at least one current electrode and a voltage between the at least one current electrode and the pair of return electrodes ; characterised in that the apparatus further comprises a pair of vertically separated additional return electrodes vertically separated from the at least one current electrode ; and wherein the processor determines from a current in the at least one current electrode, and a voltage between the at least one current electrode and the pair of return electrodes, and a voltage between the at least one current electrode and the pair of additional return electrodes a vertical resistivity of the earth formation ; wherein the apparatus is configured such that when the measurements are being made with the vertically separated additional return electrodes , the horizontally separated return electrodes are open circuited, and when the measurements are being made with the horizontally separated return electrodes , the vertically separated additional return electrodes are open circuited. <EOS>