The effects of using three different biopreparations (one natural N2 and two commercial Kl and K2) in petroleum hydrocarbons age-polluted clay soil were studied. The samples of soil were taken from refinery in Czechowice-Dziedzice and classified as heavily degraded in proportion C:N = 100:0,7. Changes after introducing biopreparations into soil (bioaugmentation), their influence on microflora development and effects of removing polluting substances were studied. Bioaugmentation did not result in intensive growth of bacterial number, which was on the control sample's level during experiment. Soil's biodegradation activity also increased in level smaller than expected.