Benz (a) anthracene (BaA), pyrene, benzo (a) pyrene (BaP), and benzo (ghi) perylene in heavy oil that had washed ashore, after leaking from a wrecked Russian oil tanker, the Nakhodka, disappeared by 99%, 92%, 60% and 33%, respectively, through the action of Mycobacterium sp. H2-5 at 30°C over a period of 20 days. This bacterium had been initially isolated as a pyrene-assimilating bacterium in 1994. PAHs in commercial heavy oil (class C) disappeared by 92%, 99%, 60%, and 10%, respectively, by the bacterium under the same conditions. The disappearance of PAHs in the two heavy oil samples by strain H2-5 was essentially to the same extent. The bacterium thus prevented any damage from the drifting of heavy oil.