On this TV segment we focused on testing if water based cleaners worked better than solvent based cleaners on concrete stones.
When done thoroughly, they didn't make much difference. What does make a difference is waiting long enough for the chemical to work, and scrubbing or rinsing before it dries out.
Also a power washer, a very hard water spray, does a lot of good in all the cleaning.
Cleaning up oil will require several attempts because the soaked in oil tends to rise up to the clean surface. Since this show, I have discoered Oil Lift which takes oil spils out of anything and actually foams it to the surface then bio-degrades it!