If you've ever violated your concrete floor with a used oil spill, you know what I'm talking about here. Found an old jug of cruddy old used oil had leaked out over a 3' square area under some cardboard boxes. (Least the cardboard kept it from running further from the immediate area. Who knows how long it was like that. Hey, it happens. Not the first time, won't be the last.
This stuff right here is the chit: http://www.homedepot.com/p/Chomp-32-oz- ... /203082110
Read the reviews on both Home Depot and Amazon. It was on the shelf at my Home Depot in the paint Department's prep materials aisle. There was so much oil after removing the cardboard and fully exposing the mess, I used cat litter first to get most all of what was on the surface absorbed. Then two applications of the Chomp, a bottle each, for the deep clean. The newer spill and most of a couple of 12 year old smaller stains are just about gone. There's one Amazon review that best describes how to actually use it for maximum effectiveness. The part about not trying to spread it around is dead on. I did that on the first application and you could see all of my swipe marks in areas still stained with oil after I scrapped it off.
For only 8 bucks, I'm going to keep a bottle on hand for little drips and spills. The sooner you get it on, the less likely for any strains to become permanent.