Applying a poultice is the best way to get oil out of granite. The poultice draws the oil back up out of the granite; the best results are achieved when the poultice is applied right after the spill.
Poultices consist of two items: an absorbent item such as diatomaceous earth, talcum powder or paper towels, and a chemical to get the stain out. In the case of oil stains, pure acetone is the best choice of chemical. Mixing the poultice until it has a consistency similar to that of putty is the first step. A layer of the mixture about 1/4 inch thick should go on top of the stain, extending about 1/2 inch around the stain in all directions. The next step is covering the whole area with plastic wrap, taping the edges down to make a seal and leaving it in place for 24 hours. The final step involves removing the plastic wrap and tape, waiting for the poultice to dry, and scraping away the paste. Repeating this process may be necessary to get all the oil out.