Removing oil stains from concrete

["Eugene D Abbondelo" <eabb@loc.gov>]

Attention Shoppers:

I remember the topic of removing oil stains from concrete has come up before, 
but I'm afraid I didn't pay much attention, but because of some recent 
"accidents", the driveway is really looking bad, and the wife has started to 
complain. So I have a mixture of really old (2+ years) stains and some new ones.

I've tried over the counter remedies from the home stores, but nothing seems to 
work.  Is there some heavy-duty, super-duper cleaner that anyone can recommend 
that works pretty well?

thanks, Gene