I have some oil stains in my exposed concrete driveway (thanks to some lazy tenants), is it best to acid wash the whole driveway with brickies acid? (hydrochloric?

Can't see how that would affect oil. Use kitty litter, the diatomaceous earth variety, leave it on for a few days.

Ed

You really need a degreaser that will soak into the concrete rather than acid

I think that will leave a stain. Maybe neat dishwash detergent... but try kitty litter first, it won't damage anything...
Ed

If you use acid you will etch surface of the the concrete except where covered with oil, therefore it will become blotchy and ruined.

Hi there are certain products that actually soak into the surface , react with the oil and purge it to the top ... doesnt leave a stain at all and an essencial part of concrete preperation before applying Concrete Colour Stains .. FYI yes acid is no good as it only works on the PH of concrete

What is this product called?

Hi Nemesis , the product i use to get rid of deep oil in floors is called Protect Crete Deni Proof , Newlook degreaser from www.getnewlook.com.au is another good product wont go as deep but you can do it over several applications and its cheap compared to Densi Proof