You could try these very cheap and easy tricks,again it depends on how old the stains are.
Mix together washingup liquid with soap power to a peanut butter paste,brush this over the stain then cover with plastic seal the edges down leave for no longer than 24hrs dont let it dry out,be careful of any bleaching might be an idea to try on a bit out the way 1st,then wash off heat would be ideal.
This has worked for me on concrette and stone b4
Or if your brave and its
new oil,drop of petrol set alight to it so to burn the oil out,this has also worked for me,dont try it on tarmac nor if the stone has been sealed
BE BLOODY CAREFULL THOUGH DO THIS AT YOUR OWN RISK
But if you want to spend money then this stuff i use
http://www.drivewaycleaning.com/?gclid=CO2wzvO8rqACFSUulAodFCkXagwith mixed results