Abstract The hydrolytic and radiolytic degradation of octyl(phenyl)-N, N-diisobutylcarbamoyl-methylphosphine oxide (CMPO) in tetrachloro-ethylene (TCE) and in tributylphosphate-TCE mixtures (TRUEX process solvent) in contact with HNO3 has been investigated. Gas chroma-tographic analysis of the degraded solutions has allowed identification and quantitation of a variety of organophosphorus degradation compounds derived from CMPO. The effect of degradation of the extractant solutions on the extraction and stripping of americium has been addressed, as has the effectiveness of Na2CO3 scrub procedures for restoring extractant performance. Extrapolation of these results to normal process application conditions indicates that neither hydrolysis nor radiolysis should compromise the americium extraction performance of TRUEX-TCE.