I use steam to start with and if this doesn't work (will only work 100% on new oil spots) I use an off the shelf product by Thompsons - 'Drive cleaner and Oil remover' I think it is called. Pour on neat, scrub in and leave for 10-15 minutes, then steam out. Have had great success with this product and it is not expensive. Many amazed customers. DON'T use on tarmac, there are other products for this.
If the mark remains, it is probably Diesel... a nightmare to shift.
Hope this helps
Andy