How big of an oil stain? How old is it? Good 'ol Dawn dish soap actually does a pretty good job. Buy the original (blue) soap, pour it on, scrub it with a brush, and hose off.
Try Dave's Insanity hot sauce... it'll remove it. You will need quite a bit depending on the size of the stain. It will even remove wax from floors.
And yeah, I'm being serious.
Use Pour-N-Restore. I've used this for almost 30 years. Use it on concrete, never on asphalt. It's a thick white liquid that smells like oranges. Pour it on the stain so it's 100% covered and let it dry. Don't touch it again. As it drys it pulls the oil and stain out. It will go to powder on its own and leave a moist spot that is just water. As it evaporates, the oil stain is gone.
It just works. I use it for new fresh drive way spots from visitors. If you're trying to remove decades of stain, it might take several tries.
If you've already tried to clean it, this may or may not get it all. If it's fresh untouched stain, this will remove 100%.
PS, I buy it in the gallon jug. Don't let it freeze in the garage and shake it up ever 4 months or so.