Brwill2005's advice is sound. A dry cleaning solvent (like Perchloroethylene) is a chlorinated hyrocarbon solvent that is commonly used to dry clean, i.e. clean without water. You need to use a hydrocarbon based solvent because your oil stain is also hydrocarbon based. Remember chemistry class where a like substance will dissolve a like substance?
It doesn't really matter that the stain is no longer fresh except that it may be harder to remove. Not knowing your exact situation, but you take the solvent and lightly wet the stain with it. You can use an absorbent terry or cotton cloth to gently blot the stain. You may need to repeat the application several times being sure to not over-wet the spots with solvent and keep blotting up the solvent until the stain lifts completely.
If you can't obtain a dry cleaning solvent, 303 Cleaner & Spot Remover would probably be your next best bet.