The essential oils of Satureja khuzestanica (before flowering & full blooming), Oliveria decumbens and Thymus daenensis collected from Ilam province, Iran, were analyzed by GC and GC-MS and evaluated for their antioxidant activity using three methods: the ferric reducing antioxidant power (FRAP), 2,2'-azinobis (3-ethylbenzothiazoline- 6-sulfonic acid) (ABTS), and 2,2-diphenyl-1- icrylhydrazyl (DPPH). All plant samples were also analyzed for total phenolic contents (TPC). The major compound of essential oils of S. khuzestanica at both stages was the phenolic monoterpene carvacrol (93.7 and 94.3 % respectively). The major components of T. daenensis essential oils were carvacrol (76.8 %), linalool (6.9 %), and trans- caryophyllene (6.3 %). The essential oil of O. decumbens was characterized as thymol (33.8 %), carvacrol (32.2 %), γ-terpinene (15.2 %) and p-cymene (14.9 %). The results obtained to evaluate the antioxidant activity and TPC showed that Thymus daenensis, Satureja khuzestanica and Oliveria decumbens essential oils can be considered good sources of natural compounds with significant antioxidant activity. For O. decumbens, a high antioxidant activity and TPC was observed, which is mainly due to the presence of thymol and carvacrol in the essential oil properties.
