Remove oil stains from concrete using household detergent, specialized concrete cleaning solutions, using a poultice or specialized microorganisms that penetrate the concrete and consume the oil. These approaches vary in effectiveness and cost.
Remove small oil spills that do not penetrate deeply into concrete using a degreasing dish detergent and water hose. Apply the detergent and water, and scrub the stain with a scrub brush. Use this approach for small oil stains.
Hardware stores offer a special concrete cleaning detergent. This alkaline material works in a method similar to other detergents, but manufacturers formulate it to loosen oily stains from concrete. Unfortunately, it is unable to remove stains that penetrate deep into the material.
Using a poultice is an effective way to draw oil stains that soak into concrete. The poultice is a mixture of an absorbent material, such as kitty litter and a solvent, such as lacquer thinner. Spread the mixture on the stain, and cover it with plastic to slow the evaporation. Leave it in place overnight, and sweep up the poultice and oil it absorbs from the concrete.
For the toughest stains, consider using the same organisms that scientists use to clean oil spills from the beach. These organisms consume crude oil and petroleum derivatives, converting them to energy for reproduction and carbon dioxide. One they consume all the oil products, they die and are harmless to the environment.