SURMMARY Origanum spp. and Thymus spp. growing spontaneously in Algeria are collected from wild populations and are sold in the local markets under the same or similar vernacular name, zaâtar (Origanum) or zhitra (Thymus). Thymus willdenowii Boiss. and Thymus algeriensis Boiss. & Reuter are mostly used as condiments while Origanum floribundun Munby and Origanum vulgare L. ssp. gladulosum (Desf.) Ietswaart are used against diarrhoea and other digestive and respiratory system disorders, as well as additive to forrage as an appetite stimulant. All four species were quite rich in essential oils; the analyses of the oils showed that all were rich in the compounds of the carvacrol pathway (p-cymene, γ-terpinene, carvacrol, thymol, and their methyl-ethers). Only minor qualitative, but considerable quantitative, variation was found within and between the species that comprise zaâtar: the major compounds of O. floribundum were p-cymene (31%), thymol (9.9%) and carvacrol (35.0%); the major compounds of O. vulgare ssp. gladulosum were γ-terpinene (13.6%), thymol-methylether (16.3%), carvacrol-methylether (11.4%) and thymol (26.1%); the major compounds of T. willdenowii were p-cymene (15.2%), thymol (15.1%) and carvacrol (51.3%); finally, from the two samples of T. algeriensis analyzed, one was rich in linalool (78.8%) and the other was rich in thymol (62.7%).