I found that oil dripped onto the drive was best removed with a biological washing powder, liberally sprinkled over the offending marks and then scrubbed furiously with a yard broom. Works reasonably well on concrete but is useless if you have a brick drive.
Gravel is, of course, best removed and replaced but she'll still spot any colour variation from what was there 6 months ago so only remove the oil stained bit and mix any new gravel in with the old. Think "The Great Escape" and the disposal of the soil dug out of the tunnels and you may have a chance.