Abstract <p>The significant volumes of hydrocarbons and associated pollutants released into the environment during the development of oil and gas resources mean that this type of pollution is becoming a priority for many oil production areas. In the Republic of Kalmykia, the soil cover is particularly strongly affected by oil pollution. The aim of this study is to determine changes in the biological properties of brown semi-desert soil, light chestnut soil, and the southern chernozem depending on the nature of the pollutant and its concentration in the soil. Zonal soils of Kalmykia were selected as objects of study. Laboratory and analytical studies, as well as sampling, were carried out using methods generally accepted in biology and soil science. The petroleum products used were commercial and crude oil, as well as fuel oil, kerosene, and gasoline. As a result of this study, it was established that the most informative soil enzymes regarding pollution by oil products are catalase and urease, the activity of which is significantly reduced and depends on the concentration of the pollutant. Phosphatase activity also decreases when contaminated with oil products, but not as significantly; invertase activity is stimulated by low concentrations of oil products and inhibited by high ones. All soils contaminated with petroleum products exhibit high phytotoxicity towards test plants, but the exception is brown semi-desert soil, in which, when contaminated with low concentrations of fuel oil and kerosene, the length of shoots and roots increases.</p>