Oxidation induction time (OIT) has been proven to be a useful diagnostic tool in assessing the extent of degradation in the polymer insulation of electric cable in nuclear power plants. Factors that influence OIT include test temperature, sample preparation, sample geometry, sample mass, particle size, thermogram interpretation, and shelf life. The effects of these parameters were investigated for ethylene propylene diene monomer (EPDM) and crosslinked polyethylene (XLPE) polymer cable insulations, which were aged in radiation and thermal environments. The results were then used to recommend standards for an OIT methodology suited for practical use in the nuclear power industry. Techniques to estimate error in thermogram interpretation and reproducibility were also developed.