Polyethylene terephthalate (PET) is the most common thermoplastic polymer resin of the polyester family that is extensively used for packaging applications due to its barrier properties, recyclability and compatibility with food applications. It can be synthesized through condensation of ethylene glycol and terephthalic acid. To improve the properties of PET, modifications can be made to create PET co-polymer (co-PET). Multi-functional pyrolyzer coupled with gas chromatography/mass spectrometry (GC/MS) is a powerful technique for distinguishing different types of co-PETs. However, the chromatogram obtained from conventional faash pyrolysis (Py) of polyester can be complicated as further degradation of the polymer can occur to produce smaller molecules such as benzene and benzoic acid. To simplify data interpretation of the pyrogram for qualitative profiling, the samples were subjected to thermochemolysis, also known as reactive pyrolysis (RxPy) in the presence of tetramethylammonium hydroxide (TMAH). In this study, a combination of evolved gas analysis (EGA)-MS, thermal desorption (TD)-GC/MS, Py-GC/MS and RxPy-GC/MS techniques were applied to study the components of different co-PETs.