The thing is, it's not a petrol "blockage" at the ports or anything. All they want you to do is not fill up on gasoline today. Funny though, because you'll end up buying the gas, just a day later. The oil companies will still receive the same amount of money. No other industry is participating. The only way it might have an effect is if all petrol consuming industries halted for a day, which is impossible.
Here in tampa the price for the cheapest gasoline (regular unleaded) is 1.95/gallon. It costs me nearly $33~ to fill my tank.
So while for others it may be "boycott gas day", for me its "no line at the pump" day.