Depending upon your persuasion, Exxon Mobil's $10.9 billion quarterly profit report on Thursday was either a wash-up or a windfall. Wall Street saw the former, questioning why the country's largest oil company couldn't grow its earnings by more than 17 percent while oil sells for more than $100 a barrel.

Both Democratic presidential candidates Barack Obama and Hillary Clinton see profits like Exxon's as excessive, and would subject them to a "windfall profits" tax to pay for programs to help Americans cope with high fuel costs.

Nothing, of course, makes a conservative economist fly off the handle like soaking wealthy oil producers. But even liberals would have a hard time defending the country's last experience with a windfall tax, in 1980.

What began as a compromise by the Carter administration to lift ceilings on oil prices grew into a bureaucratic nightmare that Congress in 1984 called the "largest and most complex tax ever levied on a U.S. industry." The law produced nowhere near the revenue it promised, made the country more reliant on foreign oil, and generated reams of red tape, according to a 2006 report by the nonpartisan Congressional Research Service.

The law was put out of its misery in 1988, two-and-a-half years before it would have automatically expired.

"It's a terrible idea today," said Phil Verleger, who helped design the windfall tax policy as the Treasury Department's director of domestic energy policy from 1977 to 1979. "The windfall profit tax was a quo for a quid; the quid was price decontrol. There's no quid right now."

Neither Democratic candidate has provided enough detail to make a full analysis of their current windfall-tax proposals.

Senator Barack Obama's campaign says he "supports imposing a windfall-profits penalty on oil selling at or over $80 per barrel" and spending the proceeds to help Americans deal with high energy prices.

Senator Hillary Clinton says she'll tax "windfall profits"—no figures are provided on how the term is defined—to pay for a temporary suspension of the 18.4-cent-per-gallon federal tax on gasoline.

Proposals like these have appeared regularly, always when oil prices have spiked.

"Everyone gets frustrated and is looking for a simple answer and a scapegoat, and the oil companies are really easy to vilify," says Gilbert Metcalf, a Tufts University economics professor and a research associate at the National Bureau of Economic Research.

President Jimmy Carter proposed the 1980 windfall tax to placate Congress as he lifted Nixon-era price controls on oil. Allowing the price of oil to rise from about $14 to the then-market price of $24 was certain to generate a windfall for oil companies, which Carter proposed should be shared with the American public.

A 50 to 70 percent tax was imposed on the market price of oil and a 1979 base price adjusted for inflation. (Technically, it was a sales tax, not a duty on excess profits.)

Today's market-driven oil-price spike makes a windfall tax a harder pill to swallow for supporters of the original policy. Emil Sunley, who was the deputy assistant Treasury secretary for tax policy in the Carter administration, noted that $110 or $115 a barrel is an "uncontrolled price" set by the laws of supply and demand, unlike the price of crude in 1980.

"There's a greater burden of proof to say this is just a pure windfall that we should tax," Sunley said.

At the time, Carter-era officials forecast that their windfall tax would generate $393 billion in gross revenue between 1980 and 1988, but it actually generated $80 billion, Salvatore Lazzari, a specialist in public finance at the Congressional Research Service, concluded in a 2006 report.

Because oil producers could deduct their windfall-tax payments from their income tax, the government netted only about $38 billion. Worse, the tax sent the U.S. oil industry into a decline. Domestic production fell somewhere between 1.2 percent to 8.0 percent during the period. Refiners shifted to foreign supplies, and imports surged.

Of course, a windfall tax could also be imposed on imported oil. But economists say that would increase energy prices much more than would a tax on domestic sales alone.

The law created an almost comical administrative burden at the Internal Revenue Service, which was suddenly faced with administering a levy on about one million businesses and people who could be classified as oil producers.

Congress created loopholes and categories that made the law a nightmare to administer. Exemptions and breaks were issued for Alaskan oil, for oil from new fields, and for oil unexpectedly coaxed from old fields.

Independent producers were taxed less than big companies, and crude from federal and Native American lands was exempt. To add to the burden, the windfall levy was amended almost every time a new tax law was enacted between 1980 and 1988.

The I.R.S. spent 11,577 staff days in the 1981 fiscal year on examining windfall taxes and another 6,335 days on training and related projects, according to a 1984 congressional study.

I.R.S. experts were forced to rule on the minutiae of the oil industry, such as choosing from among the three ways the industry was calculating the market price of Sadlerochit oil in Alaska. Case files were adding 33,000 pages of paper every two weeks, prompting a $1.8 million computer-modernization program that might be called one of the law's few lasting benefits.

The 146-page congressional report found just how woeful the situation was at the I.R.S. Tax personnel reported that oil producers frequently tried to thwart the tax authority, refusing to cooperate or creating a "multiplicity of purchases and sales and exchanges" that rendered the task of tracing the tax burden labyrinthine.

Even the appeals process was riddled with problems, since the law allowed each owner of an oil asset an individual court hearing—and it was not unusual for 50 or more people to own a single asset.

So byzantine were the windfall tax's terms that even the Supreme Court didn't want to get involved. Today's proponents might consider the court's unanimous decision to decline a challenge to the law in 1983, when the justices thrust their palms in Congress' face:

"Where, as here, Congress has exercised its considered judgment with respect to an enormously complex problem," they wrote in their opinion, "we are reluctant to disturb its determination."