On my 12 mile drive to work, I can see up to a $.40/gal difference between the prices. I don't always make an effort to buy the lowest, but it makes a difference if I do.
You see this big of a difference between different stations? If that's the idea, we never see this much variation between the brand-name vendors. The most I ever noticed was a few cents here and there unless you go to places like Safeway for gas. But when you only have three choices within 20 miles, that isn't surprising.
There is no place to get gas on my 400 foot drive to work.