As summarized in Table 3, the rank order of antioxidant potency was the same for all assays, namely, in decreasing order, Er-Rich population (most arid site), followed by Taws (least arid site) and Ourika (medium arid site) populations. All of the assessed EOs were able to reduce the stable, purple-coloured radical DPPH* into yellow-coloured DPPH-H, and oil obtained from Er-Rich population had the strongest free radical-scavenging activity with an IC50 value of 44.54 ± 0.92 μg/mL (Table 3). The lowest capacity to reduce DPPH was observed in T. saturejoides EO from population of medium arid site (Ourika) (IC50 = 204.86 ± 1.17 μg/mL). All oils were less effective than the synthetic antioxidant BHT (IC50 = 4.21 ± 0.08 μg/mL) and quercetin (IC50 = 1.07 ± 0.01 μg/mL). Similarly, Er-Rich oil exhibited the best performance in reducing power assay and β-carotene/linoleic acid assays with IC50 = 22.90 ± 0.16 μg/mL and 19.17 ± 0.01 μg/mL, respectively, but this was still lower than that of the synthetic antioxidant BHT and quercetin (