If the supply of gasoline is what it is, then the price of gasoline will be whatever it takes to limit demand to meet the supply. If that means $3.00 a gallon, then consumers are going to end up paying $3.00 per gallon, no matter what the tax is on gasoline.

This only applies to the short term: I can't back out of my friend's wedding this weekend over an extra $20 at the pump and Exxon can't refine and ship crude that it doesn't have (let alone by Saturday!). The price of gas can affect supply and demand in the long term. Which path the politicians choose may be no-effect-posturing in the short term but it has a very real impact in the long term.

Long Term Demand

My gas usage in the future is based almost 100% on the price at the pump and nothing to do with any laws outside of rationing (which no politician would do post Carter). I live near Boston and I have brothers near Philly (petedied) and DC (teddied). Meeting in Boston is a sure waste of driving time so we will either meet in Philly or DC. If the price of driving to DC or Philly is about the same we would choose based on facilities (good bars, who has horseshoe pits in the yard, etc). If the price of driving is high we will optimize for minimum miles and spend the extra money on steaks for the grill. If the cost of traveling is high enough we will put off meeting until later.

Politicians can affect my demand by either making it illegal for me to consume gas via ration coupons or by encouraging me to drive a moped via fleet MPG standards. Fleet MPG averages screw the poor because car companies must sell so many mopeds to balance out so many SUVs. The cars people actually want to purchase - even knowing the current price of gas - are at some MPG higher than the mandated average. What people want could be lower than the mandated average but then the law wouldn't need to be passed! Since GM has to hit their average and the average is below what people want GM will have to discourage people from driving SUVs by charging extra and encourage people to drive mopeds by slashing costs. This sounds great if you are a green (inconvenience == penance) but it means that poor people that would normally buy a larger car can't and rich people still get to do whatever the heck they like. It also punishes families who can't make do with a moped at any price and rewards singles who get a discount on their boxster.

No sane politician would be in favor of any of those outcomes but those are the only outcomes they have the power to legislate.

Long Term Supply

We've seen that policies affecting long term demand are political losers but there a raft of policies that affect long term supply that are political winners. Anything that cuts the profits of oil companies is a public winner because money they don't get looks like money we (the public) get to keep. The three major factors affecting supply of any good are competition, competition, and competition (this _is_ a libertarian/classic liberal blog after all). In a disaster zone the high profit from scarcity of good (aka "price gouging") causes even the non-altruistic to truck ice, batteries, and food to the area. Whatever the altruistic response you will get more stuff to the benighted area if the profiteers are allowed to come too. The current spike in gas prices isn't a localized thing so there is no Red Cross or Salvation Army funded by the many to alleviate the plight of the few. The effect of a high worldwide price of oil is worldwide (duh). Altruists specialize in the misery of the few and not the inconvenience of the many.

The expectation of profit drives investment. So much optimism and money was dumped (and lost) into US fiber optic cables that today most fiber in the us is unused ("dark" in industry speak) and dirt cheap. Massive infrastructure was built out of nothing overnight and none of it at the taxpayer's expense. The last great rush of capital stupidity was the rail roads. All the oil-can proposals both Republican and Democrat are aimed at blunting the profits of current gas manufacturers. Even worse some of the [Dem] proposals would reduce the "tax breaks" oil companies get by changing how they can account for depreciation schedules for capital. For the uninitiated in accountant-speak this means that inventing in new equipment and new wells would cost more money. Nothing would make existing companies happier than raising the barrier to entry.

There have also been threats to cap "excessive profits." You couldn't discourage new entrants into the field better if you wanted to. Who is going to step into a hugely profitable field if you know that showing up and making a profit would be grounds for going to jail? The existing players love this stuff. They already have senators and lobbyists in place and if push comes to shove they have a raft of bad years to prove they aren't jonny-come-lately-s just swooping in to screw the consumer.

Long Term Summary: Politician's View

Passing a law restricting demand is a solid loser: it won't affect short term prices and it will pain your voters short term. Passing a law affecting supply is a sure winner: it won't affect short term price but you are seen as doing something and when it doesn't work you can blame someone else. It will negatively affect long term supply but at that point the root cause is muddled and you wouldn't still be in office anyway if you had sat out the issuee.

[I'll edit in the morning for typos and grammar, but the content is about right unless I screwed up a negative]