Almost always, a full tank is a bad bet unless if you know from experience that it's the cheapest station in the area. A few years ago, I started playing the t

Almost always, a full tank is a bad bet unless if you know from experience that it's the cheapest station in the area. A few years ago, I started playing the time-domain analogue of this game (which you sort of allude to later). When gas prices are low, I keep my tank close to full. I'll stop at the gas station (which is not out of the way of my normal travels) to refill even if it's only a couple gallons. When prices are higher, I can use that reserve to ride it out and wait for prices to fall again. I don't use any more or less gas this way, but I do get a marginally better price on it.