In theory... at least one gas station would have to go: "Oh everyone is raising prices on that day!!! If I do not raise price / keep them lower, then everyone will buy at my gas station! I just have to change my gas delivery schedule a little and I can screw them all over on that day."
A friend of mine has took a franchisee from ESSO (Exxon). He sells their gas, and get one cent per litre, no matter that the price is. Pricing is done by ESSO, and he has no chance to modify the price.
He makes most of his profit with selling groceries, coffee, newspapers, soft drinks and beer.
The gas station is 24/7 open, and has a licence to sell beverages and fresh food (pizza, burgers, hot dogs...)
Cheap gas has only the effect that he sells more coffee on that day...
To attract customers he don't lower the price for gas (he can't do that anyway), but he give away for example a six pack of beer cans for the price of five cans.
His benefit is the better support (central buying of the goods for his market, marketing, loans, law and tax advices, courses in business administration) he gets from the franchiser.
Selling gas is a necessary to run such a 24/7 super market nowadays, so there are other market mechanisms more important for him than the gas price.
In Austria they have made a law that limits the time for price rises to once in a day at 12.00 am.
Australia introduced a similiar model in 2001:
http://en.wikipedia.org/wiki/FuelWatchThe German Federal Agency against Cartels made an evaluation about the fuel market in Germany an one conclusion was one problem is the market transparency.
The big company's don't hat to fix the prices by agreement, they have just to take a look at the price signs of the other company's.
3 Hours after one company has increased the price the others tend to do the same.
http://www.bundeskartellamt.de/wEnglisch/News/Archiv/ArchivNews2011/2011_10_10.phpPlanned is a governmental website for all kind of traffic information, from actual traffic jams and closed roads/bridges up to actual fuel prices - but I doubt that it would help.
The price difference is on average 5 Euro cent per litre, so a full tank (40 litre) from the cheapest gas station would be 2 Euros cheaper. That's the price for 2 hamburgers at Mc Donalds or a cup of coffee at the gas station.
Nerveless I tend to never let fall down my cars fuel under 25% - 50%, and than buy at the cheapest station.