In this work, we reviewed the effect of the solid matrix in the supercritical CO2 (SC-CO2) extraction of essentials oils from plant material. A diffusional model was adopted that assumed the substrate is as an homogeneous solid and the partition of essential oils between the solid substrate and the SC-CO2 phases is constant. The model was fitted to literature data from several plant materials (relevant solute identified between parenthesis): chamomile flowers (alpha-bisabolol), lavender flowers (camphor), oregano bracts (thymol), pennyroyal leaves and flowers (menthol), and sage leaves (1,8-cineole). Based on values of binary diffusion coefficient of the solute in the solvent (D-12) from a literature correlation, and the best-fit values of effective diffusivity of the Solute in the solid matrix (D-e) we estimated the value of the so-called microstructural factor (MF), which is defined as the ratio between D-12 and D-e which ranged from 420 for pennyroyal to 25,000 for oregano. MF encompasses several factors, mainly related with to the microstructure of the substrate, that affect the extraction rate of a solid substrate with a solvent. (c) 2009 Elsevier Ltd. All rights reserved