The effect of the pretreatment of the matrix on the CO2 extraction of essential oils and cuticular waxes from aromatic herbs was studied. The vegetable matrix, oregano bracts, was submitted to different mechanical and physical treatments prior to extraction with compressed CO2 under standard conditions (100 bar, 310 K, and 0.25 kg/h). The rates and yields of extraction of both essential oils and cuticular waxes were evaluated and compared with those obtained from an untreated matrix. The losses of essential oils during the pretreatments were estimated. Comminution under atmospheric and cryogenic conditions and comminution in a closed atmosphere (internal comminution) were the mechanical pretreatments under investigation. The physical disruption of essential oils glands by a fast decompression treatment (FD treatment) was also tested. The structure of the matrixes and essential oils glands, before and after CO2 extraction, were observed by scanning electron microscopy (SEM). Cryogenic comminution, internal comminution and FD treatment were all found to be effective matrix pretreatments for the extraction of essential oils. However, the selective liberation of the essential oils with respect to cuticular waxes obtained by the FD treatment results in a final extract with a higher content of essential oils. Moreover, the essential oils themselves are believed to be of better quality than those obtained from mechanically treated matrixes.