The same e-mail has gone around before.
"First of all, everyone's "not purchasing a drop of gasoline for one day" will not cause oil companies to "choke on their stockpiles." Oil companies run their inventories on a weekly basis, and since the "gas out" scheme doesn't call on people to buy less gasoline but simply to shift their date of purchase by one day, oil company stockpiles won't be affected at all.
Next, merely shifting the day of purchase will not "hit the entire industry with a net loss of over $4.6 billion." Consumers won't be buying any less gasoline under this "gas out" proposal; they'll simply be purchasing gas a day earlier or a day later than they usually would. The very same amount of gasoline will be sold either way, so the oil companies aren't going to lose any money at all.
By definition, a boycott involves the doing without of something, with the renunciation of the boycotted product held up as tangible proof to those who supply the commodity that consumers are prepared to do without it unless changes are made. What the "gas out" calls for isn't consumers' swearing off using or buying gasoline, even for a short time, but simply shifting their purchases by one day. Because the "gas out" doesn't call on consumers to make a sacrifice by actually giving up something, the threat it poses is a hollow one.
Not buying gas on a designated day may make people feel a bit better about things by providing them a chance to vent their anger at higher gasoline prices, but the action won't have any real impact on retail prices. An effective protest would involve something like organizing people to forswear the use of their cars on specified days, an act that could effectively demonstrate the reality of the threat that if gasoline prices stay up, American consumers are prepared to move to carpooling and public transportation for the long term. Simply changing the day one buys gas, however, imparts no such threat, because nothing is being done without."
http://www.snopes.com/politics/business/nogas.asp