Long-term corrosion behavior of T91 ferritic/martensitic steel in oxygen-doped flowing Pb–Bi eutectic is investigated by exposure for up to 20,000 h at 400 °C, 2 m/s and 2 × 10−7mass% dissolved oxygen. The corrosion phenomena and kinetics of interaction are characterized qualitatively and quantitatively. The steel shows major oxidation resulted in the formation of a bilayer Fe3O4 / Fe(Fe,Cr)2O4 scale. After 20,000 h, the scale thickness averages 12.6 ( ± 2.7) μm. The metal recession due to oxidation does not exceed 5 ( ± 1) μm. Besides oxidation, the localized dissolution of the steel is observed reaching of ∼100 μm in depth after 20,000 h.