The study involved the thermal degradation of phenolic resins in controlled atmospheres (inert and oxidizing). Its aim was to characterize volatile organic compounds (VOC) and inorganic compounds released during heat treatment. The methods used were thermogravimetry coupled with thermodesorption/gas chromatography/mass spectrometry (TG/TCT/GC/MS) and thermogravimetric analysis coupled with infrared (TGA/IR). At the end of the heat cycle, residues were characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (solid state C-13 NMR (CP/MAS)). The data show that the synthesis conditions of the crosslinked resins, the controlled environment and the temperature of the degradation heat cycle, all affect the composition of volatile compounds and residues at the end of the cycle. The data have enabled us to propose decomposition reaction mechanisms for these resins in oxidizing and inert environments.