In the present study, four separate samples of Origanum onites L., three separate samples of Satureja thymbra L., Origanum vulgare L. ssp. hirtum (Link) Ietswaart, and Thymus cilicicus Boiss. & Bal. were collected from various regions of Mugla, Turkey. The essential oils of these plants were obtained by the hydrodistillation method. Antimicrobial activities of the essential oils against microorganisms, including multiple antibiotic -resistant bacteria, were investigated using the disc diffusion method. Different antibiotic discs were used for comparison to the inhibition zones. All the essential oils used in this study were very effective against Gram-positive and Gram-negative bacteria, which included multiple resistant strains, except Pseudomonas aeruginosa ATCC 27853 and Pseudomonas fluorescens MU 87. The essential oils of the O. onites, O. vulgare ssp. hirtum, and S. thymbra were especially very effective against the resistant strains such as Stenotrophomonas maltophilia MU 64, S. maltophilia MU 99, and Chryseontonas luteola MU 65. The maximum antimicrobial activity was observed with the essential oils of O. onites. The antimicrobial activities of the essential oils varied depending on the species, subspecies, or variety. In fact, the essential oils of some plants belonging to the same species that were collected from different locations showed different levels of antimicrobial activities.