Liquid expands when it is warm, and shrinks when cold.
That is how a thermometer works.

Gas does this too.
So, why not get a little more gas for your money?

Buy gas early in the morning when it's cooler.
That cold gallon you bought will expand a little when it warms up.
Sure, the tanks are underground so the temp may not vary that much, but at these prices every little bit helps.

This may be another variable explaining our MPG discrepencies between the pump and the dash.

Need fewer troops to support.
Drive a hybrid.
Best tank 71.65 MPG.

Before this car I spent two years learning hypermiling on my 2004 HCH1.