Release of essential oils from glassy hydrophilic copolymers of 2-hydroxyethylmethacrylate (HEMA) and ethylene glycol dimethacrylate (EGDMA) was studied in a range of releasing media at 30 degrees C. The release of carvone, limonene, and eugenol was investigated using swelling-controlled release systems based on these copolymers. By changing the crosslinking ratio of the copolymers it was possible to achieve zero-order release. The amount of essential oil release was correlated to the thermodynamic compatibility of the oil-polymer pair, as judged by the solubility parameter difference.