Remove gasoline stains from concrete with kitty litter, a powdered laundry detergent paste and a nylon brush or sponge. Making sure to ventilate the area, pour kitty litter over the stains, allow it remain overnight, and remove. Then scrub the area with the detergent paste and brush or sponge.
Clay-based kitty litter absorbs stains that have not completely dried. After removing the litter, make a paste of warm water and laundry detergent that is effective against grease. Apply the paste to the stains, and allow it to remain overnight. Then scrub the stains with a brush or sponge, and rinse away the stains. Repeat the application of the paste if the stains are not completely removed.
Use muriatic acid for more difficult stains, and be sure to use eye and skin protection and secure children and animals during use.