This is just a classic case of mass hysteria. Some guy in southern Illinois starts a rumour by sending an email to his friends, who send it to their friends, etc. A certain fraction believe the rumour, and rush out to fill their tanks. Gas station operators see the long lines (and maybe got the emails too), so they figure they'd better raise prices. That lends credence to the rumour, so more people panic and rush out to fill up, raising prices still further - and probably emptying some gas station tanks.
Interesting story from the apparent epicenter here:
:: TheSouthern.com - Southern Illinois' Homepage ::
Especially interesting is the comment about halfway down, by a person who passes by a station selling at $3.69, pulls in to one down the street selling at $3.99 and fills up there, then goes back to see the other station still at $3.69 - and has the gall to complain about the station, instead of just kicking herself for her own stupidity.