Creep rupture data for the 9% chromium steels Fe9CrlMoVNb (P91), Fe9CrlMolWVNb (E911) and Fe9Cr Mo2WVNb (P92) have been evaluated using the secondary creep rate as well as the stress rupture life and compared with literature data for Fe9CrlMo (P9) and 12CrlMoV. Extrapolation procedures have been carried out in order to predict the long-terms stress rupture strengths of the 9% Cr Steels. The factors affecting the reliability of the extrapolations are discussed. The 600°C/100 000 h stress rupture strength of P92 was slightly higher than that of E911 based on data of up to 30 000h duration. The effect of oxidation on rupture life was assessed; for components of wall thickness below about 6 mm, the loss of load-bearing cross-section due to oxidation should be taken into account for service life prediction.