The Bureau of Mines analyzed vapor-aluminum-diffused stainless steels prior to conducting corrosion measurements in severely sulfidizing environments. These studies were conducted in response to the national need to better control the environmental and economic costs of corrosion. Specimens of a ferritic alloy and austenitic alloys types 316 and 310 were treated by a proprietary vapor-aluminum diffusion process and a dual vapor-aluminum diffusion process. Weights and dimensions were recorded before and after treatment, and comprehensive metallographic, x-ray, and electron microprobe analyses were conducted for both single- and dual-vapor- aluminum-diffused specimens. Surface aluminum concentrations ranged from 26 to 34 wt-pct for all alloys. Dual treatment increased the quantity of aluminum per unit area by a factor of 2 and increased the depth of penetration by a factor of 3. The aluminum-diffused region of the ferritic alloy was single-phase, afe solid solution that was ordered on the surface, whereas two distinct diffusion layers were observed on the austenitic alloys. The outer layer comprised afe solid solution that was ordered on the surface, and the inner layer was a two-phase mixture of afe solid solution and the intermetallic compound alni.