Note that there are two ways to get back to Avis at DTW, not one. The one that MileageAddict mentioned is the way that is signed when you leave I-94 -- down Middlebelt Road -- but if you come down Merriman Road (which is the road that runs directly into the airport), you can go down to the first light south of I-94 (Burton Drive, by the post office) and turn around on Merriman to get back to the rental car return area. There is a gas station at the southeast corner of the intersection where you turn around.

At RNO, there are four options within a mile of the airport or so. Three of them are on or near Plumb Lane, just west of the airport -- an Exxon station and a USA Station at or near the corner of Plumb and Harvard, and the Costco on Harvard, just south of Plumb. In addition, there is a station on the northwest corner of Mill and Terminal, north of the airport and not far from what used to be the Reno Hilton.

Mike