The use of aqueous amines, such as monoethanolamine (MEA, 2-aminoethanol), for post-combustion capture (PCC) of CO2 from fossil-fuel-fired power station flue gases leads to undesirable reactions with oxygen, SOx, and NOx. This study has used a gas chromatography with mass spectrometry detection (GCMS) method to measure the changes in concentrations of organic compounds in samples of a 30% (w/w) aqueous MEA absorbent obtained from CSIRO's PCC pilot plant operating at AGL's Loy Yang brown coal-fired power station in Latrobe Valley, Victoria, Australia. This aqueous MEA absorbent was previously used for more than 700 h of PCC, and the collected samples represent a further 834 h of PCC operation. These data provide a new perspective on the close, interdependent relationships between corrosion and amine degradation reactions. Other important outcomes include confirmation that (a) organic degradation products identified during laboratory-scale trials were also produced during pilot-scale PCC and (b) N-(2-hydroxyethyl)imidazole (HEI) is a suitable molecular marker for oxidative degradation of MEA. This investigation has also highlighted areas that require further research, including (a) determination of oxidative degradation mechanisms in both the presence and absence of dissolved transition metals, (b) determination of parameters that limit oxidative degradation during pilot-scale PCC, (c) investigation of the antioxidative or oxygen-scavenging properties of partially oxidized amine absorbents during PCC, and (d) measurement of the concentrations of glycine, glycolic acid, and other potential organic acids during PCC.