This study investigates the mechanism of incorporation of metal cations (Zn and Co) into the 316 stainless steel (SS) oxide under hydrogenated water chemistry (HWC) and On-Line NobleChemTM (OLNC). Coupons of 316 SS were exposed to simulated boiling water reactor (BWR) conditions (pure water, H:O molar ratio ∼8) at 288 °C and then analysed via surface characterisation techniques. Specifically, coupons were initially exposed under HWC conditions for 500 h, then subjected for 200 h to the OLNC treatment, and then a final exposure under HWC conditions for 500 h, all with simultaneous monitoring of the electrochemical corrosion potential. These exposures were performed both with and without Zn and or Co injection. It was found that Zn decreased the oxide thickness of the inner oxide layer and decreased the size of the crystallites on the outer layer. Addition of 0.2 ppb of Co in the water chemistry containing 10 ppb Zn did not appear to influence the oxide morphology nor its composition. Hard X-Ray XPS analysis showed that Zn did not completely suppress Co incorporation in the outer oxide layer which was still found in concentrations up to 0.6 at. % on the surface of the oxide under Zn addition conditions.