If you let kitty liter sit on it long enough, it will eventually suck the oil off the concrete. (I'm talking like 3 weeks here). I've seen it happen so don't tell me it won't work. Seth I have had good luck with using powdered laundry detergent. Wet the area and douse it with detergent. It makes a paste with enough soap and you scrub it in with a shop broom. Wash it off after 10 mins. of soaking or so. There are also industrial chemicals for the same job, but I don't know where to get them.