So...keeping track of my gas use is proving to be more difficult than I thought. An impromptu camping trip a few weeks ago messed up my count (I'm trying to determine whether, in a normal month, I can use just one tank of gas). We refilled the car yesterday, July 24th, and so I am starting the meter over once more.
Even though I've been having trouble meeting this goal, I think that my gas usage has halved since I challenged myself to use only one tank a month. It's a start.