I just added a link on the right side, see over there? --->
It's a web site that you can use, and there's an app for your smartphone, that tells you the prices of gas wherever you are, or where you're going. We use it all the time, and save anywhere from 5-20 cents per gallon. Which adds up quickly, the way we travel.
The prices come from the users. If you see one that is not listed, or has changed, you can put in the current price. You get points for reporting prices, and some number of points buys you an entry into a drawing for free gas. Which would be nice, but you've already won by using the app and not overpaying.