A method has been developed to optimise the cyanide:oxygen ratio in gold CIP/CIL circuits. A gold (96%)/ silver (4%) alloy disc electrode is placed in the leaching pulp and its corrosion potential measured against a reference electrode. The electrode is then rotated in the pulp to increase the diffusion rate of cyanide and/or oxygen to the electrode surface, and the electrode＇s corrosion potential re-measured. If the potential shifts more anodic on rotation, the gold leaching is limited by lack of oxygen, i.e. the reaction is under oxygen diffusion control. Alternatively, if the potential shifts more cathodic, then the leaching is limited by a lack of cyanide. The optimum oxygen ratio was shown to be approximately 10.5 ppm NaCN: 1 ppm O-2 (6.9:1 by moles). If either reagent is added in excess, then the portion in excess is essentially wasted. This allows for either a reduction of the reagent in excess, leading to a lower reagent consumption, or the addition of more of the reagent that is lacking, leading to faster leaching.