CO2 co-produced in brine with crude oil is the governing corrodent in upstream oil and gas systems. A potential additional corrosive species that can be introduced through ingress is O2. Consequently, strict guidelines exist within the oil and gas industry to limit O2 levels in production environments, emphasizing the significance of understanding any associated corrosion risks. These guidelines require O2 concentrations to be as low as 20 ppb, however, there is little to no experimental evidence to support this limit. The aim of the research described herein was to advance the understanding of how trace O2 concentrations can influence CO2 corrosion mechanisms of bare steel at the acidic pH of 4. Elucidating these underlying mechanisms would enable more effective corrosion prediction, thereby enabling development of effective mitigation strategies, as well as establishing validity of the aforementioned “20 ppb” guideline related to O2 ingress. To accomplish these goals, controlled experiments were performed to test aqueous O2 concentrations up to 100 ppb on pipeline steel in a CO2 saturated 1 wt% NaCl brine at 1 bar total pressure. Various electrochemical analytical techniques, including LPR, EIS, and potentiodynamic polarization measurements were employed. The research reported herein is foundational for characterizing the impact of oxygen in CO2 corrosion environments, an ongoing research activity. This will contribute to the development of more reliable and sustainable corrosion control practices for industries experiencing CO2 corrosion which can be extendable to carbon capture and transmission systems.