Taxes in 2005 equaled the previous peak year of 2000, the organization said, when by one measure 36.2 percent of gross domestic product in 30 industrial countries, including the United States, went to taxes at all levels of government.
The organization, which is based in Paris, said that when final figures are in for 2006, they will most likely show a new peak.
The report defines taxes as “compulsory, unrequited payments to general government.”
The cost of government has risen by about 20 percent since 1975, when taxes accounted for less than 30 percent of the gross domestic product of the organization’s member countries.
The increase in the ratio of taxes to gross domestic product since 2000 occurred despite cuts in tax rates in most of the countries, said Christopher Heady, head of tax policy for the organization.
But even with reduced corporate tax rates, Mr. Heady said that worldwide corporate profits had risen so sharply since 2002 that the amount of money flowing into government coffers had increased.
He attributed most of the long-term rise in taxes to expanded social insurance programs, like universal health care and pensions.
Mr. Heady said two forces were at work in the rising proportion of taxes to economic activity.
One was an upturn in world economic activity since 2002, and especially a sharp rise in corporate profits. The second factor, he said, was that while many countries cut tax rates, the cuts were made in a way that subjected more individual income to tax at the highest, albeit reduced, rates.
C. Eugene Steuerle, an Urban Institute tax economist who served as a policy adviser in the Reagan administration, said that the rise in tax receipts as a share of economic activity was not likely to last if tax rates remained unchanged.
“Growing inequality of income has added to tax collection,” Dr. Steuerle said, “but it is unclear how much of that will continue, because it can’t.”
Dr. Steuerle said the surge of revenue had helped politicians around the world put off dealing with looming future government liabilities for government-financed pensions and health care.
The greatest increase in the share of economic output going to taxes since 1975 was in Turkey and Spain, the organization said.
In Turkey, taxes more than doubled, to 32.5 percent of gross domestic product, while in Spain they nearly doubled to 36.7 percent, the O.E.C.D. calculated.
Only in the Netherlands did the share of national income going to taxes decline, down by 1.7 percentage points, to 39.5 percent of the economy.
In Italy, taxes grew from 25.4 percent of gross domestic product in 1975 to 42.7 percent last year.
A trend away from consumption taxes is also under way, Mr. Heady said, despite evidence that such taxes tend to have less of a dampening effect on economic growth than income taxes and, especially, corporate income taxes.
“The results we have to date,” Mr. Heady added, indicate “countries grow faster, all else being equal, if they make greater use of consumption taxes.” But he pointed to the United States as a paradox, noting that it has had real economic growth for more than a quarter-century even though it relies very little on consumption taxes.
“There is some evidence that countries with higher tax-to-G.D.P. ratios grow somewhat slower and have lower G.D.P. per head, controlling for other factors, but this is not a very clear relationship,” he said.
As an example, he cited Sweden, which “has the highest tax-to-G.D.P. ratio in the O.E.C.D., just over 50 percent, and yet it is one of the O.E.C.D. countries with the strongest economic performance over the past 20 years or so.”
That example, he said, showed that “a lot depends on how this money is spent.”
“Governments can spend money for all sorts of different purposes — they can spend in ways that encourage economic growth, improve the infrastructure, but there are obviously ways of government spending that does not promote growth,” Mr. Heady said.
Taxes in the United States — from the federal income tax and Social Security tax to local property levies — rose to 28.2 percent in 2006, from 25.6 percent of gross domestic product in 1975, the O.E.C.D. said. It reported that American taxes peaked at 29.9 percent in 2000, slipped to 26 percent in 2004 and then began rising again, a finding consistent with recent statistical tables released by the Internal Revenue Service.
