This study evaluates the effectiveness of bioremediation of oil-contaminated terrestrial ecosystems using a composition of organomineral ameliorants. The aim of the study is to establish the influence of ameliorants on reducing the phytotoxicity of oil-contaminated organogenic soils and to track the dynamics of the decline in oil concentration in the soil under their influence. The study is directed at developing an ecologically safe and sustainable method for cleaning soils from oil contamination, which minimizes the negative impact on the environment and contributes to the restoration of soil fertility. As a result, the optimal ratio of components of the peat-diatomite ameliorant (PDA) for activating bioremediation processes in oil-contaminated soils was experimentally substantiated. The following component ratio of PDA was recognized as the most effective for the bioremediation of oil-contaminated soils: peat 51.5-53.5 %; sapropel 31.0-33.5 %; diatomite 15.0-15.5 % (by mass of air-dry matter). A direct dependence of the efficiency of oil destruction in oil-contaminated ecosystems on the application of PDA in the recommended composition was established. The results of the research confirm the effectiveness of the developed PDA.