In the context of urgent efforts to reduce global carbon emissions, carbon capture, utilization, and storage (CCUS) has gained prominence. Tubing and casing steels are vital materials of construction (MOC) in CCUS systems, especially in supercritical CO2 (s-CO2) environments. However, the understanding of the corrosion behavior of these steels under s-CO2 conditions is limited, which presents integrity challenges. Immersion experiments were conducted with steels containing varying chromium (Cr) levels (0.5 wt% to 16.5 wt%), including P110, P91, and SS 316. These steels were exposed to s-CO2-saturated brine water (3.5 wt% NaCl) at 50 °C and 10 MPa for durations of 10 and 100 hours. Corrosion rates were determined via weight loss measurements, and corrosion products were analyzed with SEM and XRD. P110 displayed the highest corrosion rates (15.7 mm/y at 10 hours, 2.9 mm/y at 100 hours) but developed a thick FeCO3 layer after 100 hours. In contrast, P91 and SS 316 exhibited lower corrosion rates after 100 hours (0.04 mm/y and < 0.01 mm/y, respectively). The influence of Cr content and exposure duration on the corrosion behavior of these steels were discussed. All steels exhibited decreasing corrosion rates over time, primarily due to oxide formation, enhancing the understanding of casing and tubing steel corrosion in s-CO2 environments.