Oregano herbs and essential oils are considered of great interest for their medicinal virtues as well as for their culinary properties. The present investigation aims to study the chemical diversity of the essential oils (EO) of a rare Origanum species (O. grosii) endemic to the NorthWest of Morocco based on a large sample size (68 individual plants from 8 natural populations). Besides, 8 individual plants (genotypes) with defined EO yield and composition have been transplanted in the experimental field to show the impact of changing environmental conditions on their EO characteristics. All EOs samples were analyzed by Gas Chromatography with Flame Ionization Detector (GC-FID), Gas Chromatography/Mass Spectrom-etry (GC/MS) and Nuclear Magnetic Resonance (13 C NMR). The EO yields of O. grosii extracted by hydrodistillation ranged from 1.71% to 2.41% with an average of 2%. The analysis showed that chemical profile of O. grosii from natural accessions is dominated by carvacrol (0.48-85.66%), p-cymene (3.01-77.49%), thymol (0-75.56%) and γ-terpinene (0-28.9%), and to a lesser extent with thymohydroquinone, thymoquinone and carvacryl methyl oxide in some individual plants with remarkable intraspecific and intrapopulation variability. The EO production of the transplanted genotypes was positively affected by the experimental field conditions. In addition, the transplantation induced changes in the chemical composition of their major components (γ-terpinene, p-cymene, carvacrol, thymol and thymoquinone) where we stated mainly an increase of γ-terpinene and carvacrol against a decrease of p-cymene. The present findings exhibit the chemical profile of O. grosii in relation with their geographical origins, besides they provide useful data concerning the impact of the culture on their EO characteristics.