Measurements and data are reported for the total hemispherical emissivity of Grade 91 steel [ASTM International (ASTM) A387 Grade 91] for the temperature range of 400 K to 1048 K using ASTM standard C835-06. The surfaces studied included (1) an electric discharge machining (EDM) cut, (2) Grade 91 steel sandblasted with 320-grit-sized alumina beads, (3) EDM-cut Grade 91 steel oxidized in air, and (4) Grade 91 steel sandblasted with 320-grit-sized alumina beads and oxidized in air. The EDM-cut Grade 91 steel was oxidized at 873 K and 1023 K for 1, 3, and 5 h. The 320-grit sandblasted Grade 91 steel was oxidized at 1023 K for 5 h. Air oxidations were carried out in a three-zone furnace at fixed airflow. It appears that under some conditions, Grade 91 steel can reach the emissivities required for passive heat removal during an air ingress accident.