Ferritic stainless steels currently used as the interconnect materials in solid oxide fuel cells do not exhibit adequate electronic conductivity over expected periods of service. In addition to the relatively poor conductivity of the oxide scales, the metal-oxide scale interfacial defects contribute to significant conductivity losses. In this work, the metal-oxide scale interfacial defects are studied for two grades of stainless steels, AISI-SAE 430 and ZMG232. Scanning electron microscopy, as well as surface science analysis techniques including Auger electron spectroscopy, X-ray photoelectron spectroscopy, and secondary-ion mass spectroscopy, was used to study the metal-oxide scale interface for AISI-SAE 430 and for ZMG232 coupons. Oxide scale spallation occurred during rapid cooling of oxidized AISI-SAE 430 steels. Large, micrometer-sized cavities appeared beneath the spalled scales on AISI-SAE 430. The metal substrate is not in contact with the scale in these locations. Moreover, for this steel, nonmetallic and metallic impurities, such as Si, S, Cl, N, F, Pb, V, and Al, segregate at the metal-oxide scale interface and result in reduced metal-to-scale adhesion and contact area. However, no marked impurity segregation and spallation occur for ZMG232, which contains Zr and La as reactive elements that prevent impurity segregation.