Extraction tests were undertaken using supercritical carbon dioxide at 100 bar and 313 K on the model herb Origanum vulgare L. ssp. virens (Hoffm. et Link) letswarrt in the presence of water. An increase in the extraction degree of essential oils was noted when water was added in either a discontinuous or a continuous manner. The largest increase was observed when water was added discontinuously at a concentration of 80% w/w. The discontinuous addition of water also led to a reduction in the yield of the coextracted waxy material. In contrast, the continuous addition of water led to an increase in the yield of waxy material. The increase in the degree of extraction of the essential oils from the plant matrix was largely due to interactions between the modifier + fluid + matrix, which was confirmed by experimental tests on an inert matrix. Vapor-phase data for the CO2 + carvacrol + water system from 80 to 320 bar at 313 K are also given.