The aim of the work was to investigate corrosion resistance of highly alloyed steels and Ni-based alloys in a steam atmosphere for 1000 h at 700°C. In these steam oxidation experiments, two solid solution strengthened alloys; Haynes Ò 230 Ò , 617 alloy, two gamma-prime (c 0 ) strengthened alloys; 263 and Haynes Ò 282 Ò and three Cr?Ni-rich stainless steels: 309S, 310S and HR3C austenitic steels were exposed. The study showed that the materials exposed commonly developed thin oxide scales; in Ni-based alloys, these consisted of mainly MnCr 2 O 4 spinels and Cr 2 O 3 , with the exception of 617 alloy where NiCr 2 O 4 spinels and Cr 2 O 3 were found. In Fe-based alloys, Cr 2 O 3 , MnCr 2 O 4 spinels, Fe,Mn(SiO) 4 , and finally Fe 3 O 4 developed. No evaporation of chromia has been found within 1000 h test period. Furthermore, the development of TiO 2 was not observed into a large extent in Haynes Ò 282 Ò and 263 alloy, in contrast to the study performed at 800°C under the same steam environment conditions.