The stability of silica impregnated with commercial tetraethylenepentamine (TEPA) under accelerated oxidizing conditions was evaluated, and the changes in the composition of sorbents during oxidative degradation were first reported. The oxidative stability of sorbents depended on the TEPA loading, oxidation duration, temperature, and O-2 concentration. The marked loss of the CO2 adsorption capacity of the sorbents in O-2-containing environments was mainly caused by changes in the functional groups of TEPA and the sorbent composition, as supported by thermogravimetric, elemental, infrared spectroscopic, and gas chromatography analyses. The results suggested that the hydroxyl groups of silica help to protect TEPA from oxidation. The pore and surface characteristics of sorbent have a significant influence on the O-2 diffusion, regulating the oxidation rate. Among isolated components in commercial TEPA, 1,4,7,10,13-pentaazatridecane, 4-(2-aminoethyl)-N-(2-aminoethyl)-N'-[2-[(2-aminoethyl)amino]ethyl]-1,2-ethanediamine, and 1-[2-[[2-[(2-aminoethyl)amino]ethyl] amino]ethyl]piperazine were revealed to be sensitive to O-2, whereas 1-(2-aminoethyl)-4-[[(2-aminoethyl)amino]ethyl]piperazine displayed strong O-2 resistance.