The white rot fungus Agaricus campestris collected from the wild in Lagos State Nigeria was cultured in minimal salt medium (MSM) contaminated with engine oil with the aim of investigating its degradative potential. The Indiscriminate disposal of spent engine oil by motor mechanics and other workers in Nigeria necessitated this research. The mushroom was grown in minimal salt medium for 30 days with the engine oil as its sole carbon source. The optical densities at 530 and 620 nm of engine oil contaminated MSM seeded with A. campestris and engine oil contaminated MSM not seeded with the mushroom was recorded for 30 days. There was significant difference between the optical densities of the two treatments with the contaminated MSM seeded (with A. campestris) been higher (p<0.05) at day 25. Total residual petroleum hydrocarbons were extracted at the end of 30 days with n-hexane and analyzed with gas chromatography attached to a flame ionizer detector (GC-FID). Agaricus campestris significantly reduced the total petroleum hydrocarbons from 2744.72 mg/l in control to 503.08 mg/l in the contaminated minimal salt solution (p<0.05) (i.e. over 90% of petroleum hydrocarbons were degraded). There was formation of secondary metabolites shown by repeats of some carbon atoms not found in the control. The fungus was able to mineralize long chain carbon compounds within the C24-C28 range as some of them disappeared from the seeded contaminated MSM. This research work concludes that Agaricus campestris has potential for mycoremediation of engine oil contaminated sites. There is need for more research to be done to establish the growth of the fungus in soils contaminated with engine oil.