Depends on where you are coming from. Here's a parking lot map that might help. http://www.flychicago.com/ohare/park...e/parking.shtm

Locate Bessie Coleman Dr. in the middle of the map - that's where Hertz (and most others) return area is. There are a lot of options for gas stations along the way, but if you want to start from here, follow Bessie Coleman north and take a right at the end of the road and then a quick left on Mannheim Road. You can take Mannheim north a few miles or hang a right on Higgins and follow it east a few miles.