My guess is that these places either have more poor people, or not enough small commercial areas. I've lived in Wyoming, and there's like one convenience store per town and nothing else. So you have to drive forever to get to a clump of stores and shit. I've rode through most of the western US and have been in Texas, New Mexico, and spent a summer in one of the Dakotas (they're both pretty much identical). The states on this map with the highest gas expenses are the most fucking boring. The eastern ones shown in darker piss here, don't seem to suffer from low population density, but maybe they suffer from more lower income earners instead. Damn poor people driving to Wall-mart all the time.

Actually, what we need here is an overlay of a US map that shows how far people are from the nearest Wall-Mart.