At 1000+ miles per tank I go for a month at a time between fuel purchases. I'm doing my bit, you slackers!
So what would happen? Station owners would see a drop in the day's receipts. Since they already bought the fuel from the suppliers, the suppliers couldn't give a ship less if you or I don't buy. They already have the day's percentage of the umpteen billion they earn a year.
Slurpee sales and state lottery receipts would be down, more day old hot dogs would merrily spin for another night. Twinkie's would lose about 1/5000th of their remaining shelf life. Other than that? Not a thing.
Let's stop human CO2 emissions! Everyone hold their breath for 20 seconds at noon GMT!
As others have pointed out, this can't (even in theory) work. And historically (on years when it's been tried) it didn't in fact do any good.
The reason this can't work, is that it does NOTHING to lower overall usage (which might effect "supply and demand"), and merely shifts the purchasing to a different day. And worse yet, because people didn't spread out usage out as evenly (because people were trying to skip buying of gas on this day), it actually has the potential to cause a slight spike in demand on days around the 15th (thereby actually causing prices to go up a little)!
IMHO this is a cute "feel good gimmick" only. The only positive things that this could possibly do (even if all goes well), is possibly get a few more people thinking about gas prices and/or send a "symbolic message" that people are "serious" about this issue. But more likely than not, the only message this will really send, is that people are stupid sheep that can't really do anything that matters. And the whole premise of this exercise (in futility), is so flawed, that (far from getting people to think) it has the significant danger of distracting from other things that might actually do some good (for example, techniques to get better gas mileage, and therefore have to use less overall gas)...
Here's an idea, pick a country at random and figure out how much gas is there and next time you buy gas put the amount you save by living here in your bank account...
every time the price of gas goes up, it makes me smile, they are doing what a buissness is ment to do, making money, oil compenys are not running a charity, they didn't go in to the industry out of the kindness of their hearts, if they don't do everything they can to make a profit then they are violating the first law of buissness, "make as much money as possible for your share holders" if you don't do that as a buissness you have failed.