This is one strange debate the candidates are having on energy policy. With gas prices close to $4 a gallon, Hillary Clinton and John McCain say they'll bring relief with a moratorium on the 18.4-cent federal gas tax. Barack Obama opposes that but prefers a 1970s-style windfall profits tax (as does Mrs. Clinton).

Mr. Obama is right to oppose the gas-tax gimmick, but his idea is even worse. Neither proposal addresses the problem of energy supply, especially the lack of domestic oil and gas thanks to decades of Congressional restrictions on U.S. production. Mr. Obama supports most of those "no drilling" rules, but that hasn't stopped him from denouncing high gas prices on the campaign trail. He is running TV ads in North Carolina that show him walking through a gas station and declaring that he'll slap a tax on the $40 billion in "excess profits" of Exxon Mobil.

The idea is catching on. Last week Pennsylvania Congressman Paul Kanjorski introduced a windfall profits tax as part of what he called the "Consumer Reasonable Energy Price Protection Act of 2008." So now we have Congress threatening to help itself to business profits even though Washington already takes 35% right off the top with the corporate income tax.

You may also be wondering how a higher tax on energy will lower gas prices. Normally, when you tax something, you get less of it, but Mr. Obama seems to think he can repeal the laws of economics. We tried this windfall profits scheme in 1980. It backfired. The Congressional Research Service found in a 1990 analysis that the tax reduced domestic oil production by 3% to 6% and increased oil imports from OPEC by 8% to 16%. Mr. Obama nonetheless pledges to lessen our dependence on foreign oil, which he says "costs America $800 million a day." Someone should tell him that oil imports would soar if his tax plan becomes law. The biggest beneficiaries would be OPEC oil ministers.

There's another policy contradiction here. Exxon is now under attack for buying back $2 billion of its own stock rather than adding to the more than $21 billion it is likely to invest in energy research and exploration this year. But hold on. If oil companies believe their earnings from exploring for new oil will be expropriated by government – and an excise tax on profits is pure expropriation – they will surely invest less, not more. A profits tax is a sure formula to keep the future price of gas higher.

Exxon's profits are soaring with the recent oil price spike, but the energy industry's earnings aren't as outsized as the politicians seem to think. Thomson Financial calculates that profits from the oil and natural gas industry over the past year were 8.3% of investment, while the all-industry average is 7.8%. And this was a boom year for oil. An analysis by the Cato Institute's Jerry Taylor finds that between 1970 and 2003 (which includes peak and valley years for earnings) the oil and gas business was "less profitable than the rest of the U.S. economy." These are hardly robber barons.

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