aside: There is a mpg thread floating around somewhere thats relevent to this.

In answer to your question: I generally get 300 miles until the light comes on. I usually drive it for 10 to 20 miles after that and fill up 13.0 to 13.5 gallons. The most I have put in was 14.3 pretty close to the last hatch. 15.9 gallons sounds accurate for the tanks capacity.