Molly, go to your local garage workshop and enquire what they use on garage floors and other industrial places where the floors become contaminated with oil and grease. I have used it myself but can not think of the name. IT works on the same principal as the cat litter but has special properties. The only thing is you will have to use it in a dry spell.There are also comercial detergents available that would help, phone a local fuel oil supplier. My experience is that you will never get rid of the stain completely unless the offending patch is dug up and replaced. What about a claim on your house insurance. Who spilt it, if it was not you who did and are they insured. Good luck.JTS.