Abstract: A method and apparatus for using cathodic currents from individual electrodes of a multielectrode sensor to indicate how safely a pipe in soil, or a metal structure in an electrolyte, is cathodically protected. This method uses a simple parameter derived from the multielectrode sensor, called cathodic protection effectiveness margin, or CPEM, to indicate and control the cathodic protection (CP) system so that the CP operates within the optimal range. This method is solely based on the measurements of currents and eliminates the reference electrode that has been one of the most important components in the present CP practice.