A federal study requested by Sen. Byron Dorgan, D-N.D., reported last week that two-thirds of U.S. corporations pay no federal income tax. The study produced, as they say, more heat than light.

Bold headlines fueled outrage over big corporations getting away without paying their fair share of taxes. That's understandable, because when companies — or individuals — do not pay their fair share, it increases the tax burden on others.

And Dorgan, too, expressed outrage, saying, "It's time for big corporations to pay their fair share."

But the study, conducted by the Government Accountability Office (GAO), didn't go far enough. Detailed explanations of how and why corporations avoid paying taxes should have been part of the report.

A few explanations were offered, but the corporate scofflaw message dominated the news.

One analyst noted that a significant number of smaller, typically family owned businesses operate as a so-called "S"corporation under the federal tax code. The rules for "S" corporations differ from those of the more common "C"corporations in that profits are attributed to the shareholders and federal taxes are paid through the personal income tax returns of the shareholders.

The GAO report should have noted the amount of taxes being paid in this fashion that do not show up as corporate income taxes. If the "S" corporation factor is significant, the report should have provided that information.

Other analysts noted that some very large corporations paid no taxes because they lost money. Some lost lots of money.

Commenting on the GAOreport, and the associated outrage by Dorgan, the WallStreet Journal editorialized, "Among the large companies (those with more than $250 million in assets or $50 million in sales)that paid no taxes, 85 percent of them made no profits that year. American Airlines and General Motors escaped income tax for 2005 through the clever tax dodge of losing $862 million and $10.5 billion, respectively. How unpatriotic."

One potential explanation that was mentioned in the report was potential abuse of something called "transfer prices," which are the prices charged between two parts of a large company, such as the parent company and a subsidiary. Dorgan and others have long complained that some large multinational companies manipulate transfer pricing to shift income from the United States to foreign countries, where the tax rates are almost always lower.

The study did bring up the point that the top 35 percent corporate tax rate is second-highest after Japan's, and that has already become an issue in the presidential campaign.

If this abuse is occurring, it should be exposed and those companies abusing transfer pricing should be forced to pay taxes on the true profits made in their U.S. operations.

Finally, a largely unspoken explanation for some of the corporations not paying corporate income taxes is probably loopholes and special provisions written into the ridiculously complex federal tax code by Congress.

Dorgan, and every member of Congress, should look in the mirror if they want to know how the federal tax code has become so riddled with tax loopholes. Too many members of Congress do the bidding of corporate interests that help fund their re-election campaigns when it comes to inserting special favors in the tax code.

Revealing how tax loopholes and targeted tax breaks have contributed to only one-third of U.S. corporations paying corporate income taxes would have made the GAOreport useful. Without further investigation, the report appeared to be little more than fuel for some subtle business-bashing and political grandstanding.

The Associated Press article on the corporate tax study said, "The GAOstudy did not investigate why corporations weren't paying federal income or corporate taxes." Why not?

Without examining the reasons behind the story, the Senate-commissioned GAO study makes for some senational headlines but doesn't do anything to help ensure that all corporations are paying their fair share of taxes. Without more details or a followup report, Dorgan's study does more to inflame than inform and fails to offer guidance on how to make corporate taxes more fair.