The influence of deposits of CaO, CaSO4, and MgO on the oxidation behavior of a number of Cr2O3-forming and Al2O3-forming alloys was studied over the temperature range 850‡ to 1050 ‡C. Deposits of CaO were observed to accelerate the degradation of Cr2O3-forming alloys in oxvgen or air by two mechanisms: (1) accelerated CrO3 evaporation over the entire temperature range studied; and (2) liquid formation by reaction between CaO and Cr2O3 at temperatures above 1000 ‡C which resulted in catastrophiccorrosion. The reaction of transient Cr2O3 with CaO also resulted in liquid formation on Ni-Cr-Al and Co-Cr-Al alloys, which are nominally Al2O3-formers, and produced severe corrosion. Deposits of CaSO4 did not accelerate corrosion by either mechanism. Deposits of MgO enhanced degradation by mechanism (1) but not by mechanism (2), since there are no low melting phases in the MgO-Cr2O3 system. Chromium-free Ni-Al alloys resisted attack by either mechanism.