I agree with EvMac - we need a predictable "floor" for prices, which will create a sustained economic incentive for viable alternatives to fossil fuels. It should really be a lot broader than a gas tax, though.

It is essential that the revenue from such essential taxation be prohibited, by "lock box" law, from being used for road widening. Indeed, much of it should be used to restore the livability and compatibility of oversized roads by funding travel lane removal ("road diets").

A gas tax would bolster the economy, reduce dependence on foreign oil, and promote conservation and alternative energy. A $1/gallon increased tax would raise $150 billion yearly, which could help expand health care and education. The pump price would go up much less than the tax due to lower crude oil prices. The tax could overnight turn the bear market into one of optimism for the US economy.

A fuel tax of 1USD/gallon over the next 10 to 15 years would pay the US debt for the wars in Iraq and Afghanistan.

Here is my alternative idea with a more comprehensive approach than only raising the gas tax.

http://obamaurbanpolicy.uservoice.com/pages/general/suggestions/71904

We need to start looking beyond just gas taxes. We need vehicle miles taxes, because that is what actually creates the infrastructure expense. If you have a prius and an equivalent conventional car, the conventional car now pays more for roads even though the heavier prius does more damage to the road. We should also be taxing for vehicle weight as well.

Establish a minimum price per gallon, and tax it up to that point. When the price of gas goes up again (and it will), bring it up again to the next quarter, and so on.