The nodular corrosion susceptibility of two zirconium alloys, namely Zr-2.5Nb and Zr-2.5Nb-0.5Cu, in CO₂ + O₂ containing different contaminants is established. The contaminants used were ethylene, chlorine, formic acid, nitric acid, sulphuric acid and moisture. Nodules formed on both alloys in presence of each contaminant with varied extent except for sulphuric acid. The presence of ethylene resulted in nodular corrosion only in presence of radiation. The occurrence and extent of nodular corrosion is discussed in light of the “global mechanism”for nodular corrosion of zirconium alloys in gaseous environments.