Speaking of topping off, I learned this about the Civic GX natural gas vehicle:

"If driven from LA to Washington DC, the GX would emit less pollution than spilling a teaspoon of gasoline on the ground."

Pretty amazing, huh?

Anyway, on the 700 mile thing - I have seen in my car that I usually have about 1.5 to 1.75 gallons left when the "low fuel indicator" comes on for the first time. So even taking a conservative number of 48 MPG, I believe I can get AT LEAST 72 more miles. Many times, my low fuel warning light will come on, then on a later driving session it will again turn off. I have two tanks over 700 MPG for far, with the 13.2 gallon tank !! Good Luck All !!!