An open circuit reference electrode (OCRE) has been incorporated in a potential – control circuit to measure passive current (corrosion rate) during the usual noble drift of corrosion potential. This technique permits current measurements in the early stage of passive film formation and allows subsequent continuous – time measurements of film growth kinetics in the absence of artificial constant potential control. Corrosion potentials and corrosion rates are presented for type 304 austenitic stainless steel (304 SS) and nickel base alloy 22 in sulfuric acid solution for comparison with prior work. Mott- Schottky measurements showed that passive films on each alloy have similar semiconducting properties whether formed by dissolved oxygen or maintaining a constant passive potential using a potentiostat..