I have squeezed in almost 16.5 gals into my xfire one time. It was a really hectic week with long hours so I basically came home, ate and crashed, got up and did it all again the next day. Stopped at a gas station on the way home that friday, after having driven 2 days with the light on. She was thirsty for suuuuuure!

By the way, the whole running with your tank always low causing clogged fuel filters/burnt up fuel pumps is a myth. Fuel pumps pull fuel from the absolute lowest point in every fuel tank 100% of the time. The particles that happen to be in the tank typically float slightly off the bottom of the tank (from less than 1/8th" to around 1") and slosh around with every change of direction the car makes, causing the particles to flow back and forth across the pick-up sock. Running the tank low has no effect on what gets picked up because what little is there is always at the bottom anyway.