Oil sands crude from Canada pollutes less than previously calculated, according to an Alberta government report.

Carbon-dioxide emissions from oil produced in western Canadian are about 10% higher than other US crude imports, the Alberta Energy Research Institute said in the report. Earlier studies found the greenhouse-gases emissions were as much as 40% higher.

Canadian player Nexen and supermajor Shell are among oil companies that face possible import barriers into the US under new environmental rules being considered in Congress aimed at limiting emissions from gasoline and other transportation fuels.

Canada sells about 60% of its oil sands crude to US refineries.

“This is a critical issue for the future of oil sands,” Dan Yergin, chairman of Cambridge Energy Research Associates said in an interview with Bloomberg.

“What is the overall net impact on CO2 compared to other oils?”

The Alberta institute report, to be released later today to the public, uses new models to calculate carbon emissions from oil produced in nations such as Saudi Arabia and Venezuela where operational information may not be readily available, said Eddy Isaacs, executive director of the group.

The energy used in injecting water into wells to coax out more oil, for example, is included in the new calculation.