I gave up on that a decade or longer ago. I realize that $5 a week adds up but the inconvenience of running out of fuel one time makes up for years of savings. Not to mention possible mechanical issues that may occur due to running out of fuel.
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Oh yeah, been using GasBuddy for years. The double edged sword is that it can tempt you to try to stretch your fuelups: "If I go 20 more miles I can save a dime a gallon!"