[en] Uniaxial creep strength of the martensitic steel T91 in static LBE at ≤10⁻⁷ mass% dissolved oxygen and air at 450–550 °C has been studied. To study an effect of loading, corrosion tests were carried out in LBE at c_o ≥ 10⁻⁷ mass% additionally. Experiments in LBE at 450 °C show that time-to-rupture of T91 is longer than 23,711 h at 390 MPa and c_o = 10⁻⁷ mass% and not shorter than 8900 h at the same load and significantly lower oxygen content. Thin protective oxide film forms on T91 in LBE in the c_o-range between 5.0 × 10⁻¹⁰ and 1.9 × 10⁻¹³ mass% at 500 °C while increasing of the test temperature up to 550 °C resulted in simultaneous solution-based corrosion attack and an internal oxidation on surface in the crept T91 in the c_o-range between 1.0 × 10⁻⁸ and 7.1 × 10⁻¹¹ mass%. The results of post-test evaluations are presented and discussed with a link to the in-situ measured oxygen concentration.