I've used the kitty litter/floor dry method a lot over the years. Works pretty good for the most part on a recent spill. A spill that has sat longer and has had a chance to set into the concrete (trans fluid is the worst) are the ones that can come back to haunt you. The first time you get conditions that allow the floor to sweat, it will lift some of the oil residue out of the concrete pores and it's as slippery as ice. Use TSP on the stubborn spot and it will lift it out. Most paint stores and hardware stores sell it. (Tri Sodium Phosphate) is what TSP it stands for. You see it sold in folded up cartons like 1/2 pint and 1 pint milk cartons. Ventilation, rubber gloves and common sense are called for when using this stuff...but it does work well.