Absorb Surface Material

• Before you attempt to deep-clean the concrete, get the stain off the surface. Even if an oil stain appears to have completely soaked in and dried, you'll usually find (by running your fingertips over it) that some is still sitting on the surface. Wiping at oil is only going to grind it into the concrete so, instead, cover it with an inch-deep layer of standard clay cat litter and let it sit for at least 24 hours. The dried clay in the cat litter is a natural sponge, pulling the oil and grease upward and into the clay. After a day or two, shovel up the oil-soaked litter.
  
  

Deep Clean

• There are several ways to clean deep-seated concrete stains that remain after you've cleaned the surface. Which method works best depends largely on the type of concrete and the nature of the stain. Try one or more of them until you find what works. Start by hosing down the whole concrete area. Sprinkle laundry detergent over the stain, let it sit for an hour, then scrub it in with a bristle brush and hose it off. If that doesn't work, try a bleach solution (1 cup bleach to 1 gallon of water), scrubbing it on and letting it sit for an hour. You can also try TSP (trisodium phosphate), a heavy-duty powdered cleaner that you mix with water. Make sure the floor is thoroughly rinsed of all other cleaning agents before you start, and follow the instructions carefully
  
  

Seal the Concrete

• Once you've gotten the stain up, scrub the concrete well with liquid dish soap, rinse, and let it dry thoroughly. When it's completely dry, buy a penetrating sealer to help prevent future stains. The sealer is spread on with a brush or other method (see the instructions on the sealer you buy), and it provides a barrier against both moisture and stains. Make sure you're satisfied with your stain-removal success before you seal it, or you'll be sealing in the stain.