Try this: Go to Lowe's and buy some Muriatic Acid. Very, very carefully mix in a garden hand water sprinkler (mix water and Muriatic Acid). Put the water in first then add the acid so it doesn't splatter on you. If you do get some on you, rinse immediately with some cold water from a hose. Sprinkle the mixture over the oil stain. You should see it fade. Do it again and it will fade even more.
