EUGENE, Ore. -- Gasoline refined in the Pacific Northwest contains the nation's highest levels of benzene, a pollutant linked to leukemia.

New federal rules would cut the level nationally but would still leave Northwest gasoline with more benzene than in other parts of the country, the Register-Guard newspaper of Eugene reported.

"There's a clear connection between benzene exposure and cancer," Merlyn Hough, director of the Lane Regional Air Protection Agency, told the paper.

He said studies show that benzene in the air mainly comes from vehicle exhaust; that benzene levels in exhaust fumes are related to benzene levels in gasoline; and that benzene levels in the air relate to cancer in humans.

The federal Environmental Protection Agency proposed the benzene reduction rule in February. The plan was to cut the average of benzene content in gasoline nationally from 0.97 percent to 0.62 percent by volume.

In comparison, Northwest gasoline has 2.06 percent benzene content. The new rule would cut that to 1.04 percent.

The new rules would go into effect in 2011.

In the mid-1990s, the EPA required some cities, and encouraged others, to switch to reformulated gasoline, which contains fewer polluting chemicals, including far less benzene.

But in the Northwest, where the air was relatively clean, it did not force refineries to upgrade.

In some places, refineries produce gasoline with as little as 0.29 percent benzene, and the East Coast and Southern California burn cleaner gasoline than the Pacific Northwest.

The EPA figures that 88 of the country's 115 refineries would have to upgrade as a result of the proposed rule.

It concluded that Northwest refineries would be able to take advantage of a credit system, in which they buy the right to continue producing gasoline with above-level benzene content.

"Benzene is carcinogenic. It's cheap to regulate -- less than a penny a gallon -- and technologies exist to limit it substantially," said Bill Becker, executive director of the Washington, D.C.-based Association of Local Air Pollution Control Officials.

Northwest air officials asked the EPA for tougher regulations that would get Northwest refineries closer to the national standard.

"Allowing Pacific Northwest refiners to continue to produce fuel with the highest benzene content in the country puts Oregon citizens needlessly at risk," wrote Andrew Ginsburg, administrator of the air quality division of the Oregon Department of Environmental Quality.

Requiring all refineries to meet the proposed lower standard would cost industry too much, said John Millett, an EPA spokesman. "EPA couldn't just give a blanket cap without a cost or feasibility justification," he said. "It's reality."

An EPA analysis estimated an average upgrade cost for each refinery at $6 million.

Al Mannato, a manager at the American Petroleum Institute, an industry group, said industry estimates show it could cost an individual refinery two or three times that much.