Postponing the purchase of gas is unlikely to have any telling effect.
If
all users did not go to the pump on the 15th, it would take
$2,292,000,000.00 (that's almost 3 BILLION) out of the oil companies
pockets for just one day
. . . and 2($2,292,000,000.00) the next day
You want gas prices to be lower? Drive less and support alternative fuels.
For your reading enjoyment: The Snopes take:
http://www.snopes.com/politics/gasoline/nogas.asp