Experimental studies have been carried out on the degradability of monoaromatic hydrocarbons (benzene, toluene, and ethylbenzene) and phenols (phenol, pyrocatechol, hydroquinone, tetrachloropyrocatechol) by bacteria isolated from coastal waters and soils of the Absheron peninsula at the Caspian Sea. It has been shown that the degradation of pyrocatechol, in particular, by Pseudomonas sp. bacteria occurs with the cleavage of the aromatic ring in two directions (in the meta- and ortho-positions), and that of tetrachloropyrocatechol involves the cleavage of the aromatic ring in the ortho-position and the formation of tetrachloromuconic acid. By reversed-phase high-performance liquid chromatography, more than ten individual compounds were detected and identified in the biodegradation products under the test conditions. It has been also shown that mainly linear functional compounds formed by aromatic ring opening in the meta- or ortho-position are found in the case of pyrocatechol and hydroquinone.