Hi, Ernest!  I am not so knowledgeable about the mechanics of biodegradation of oil-polluted soils in general.  What I am so interested to share with you, though, is the existing study done by an American mycologist Paul Stamets showing that mushrooms can easily consume the oil load in oil-polluted soils.

You may try reading some links.  I hope this will help you somehow.  More power on your research.  

http://www.fungi.com/blog/items/the-petroleum-problem.html

http://www.wsdot.wa.gov/research/reports/fullreports/464.1.pdf

http://www.fungi.com/blog/items/the-petroleum-problem.html

Thanks Jennifer.