'It is important ... that the process rely on factual information and be in keeping with the free trade principles that have served our energy relationship so well over the past quarter century,' wrote Alberta Premier Ed Stelmach. 'It is important ... that the process rely on factual information and be in keeping with the free trade principles that have served our energy relationship so well over the past quarter century,' wrote Alberta Premier Ed Stelmach. (CBC)Alberta Premier Ed Stelmach defended the TransCanada Keystone XL pipeline in a letter sent Wednesday to U.S. Secretary of State Hillary Clinton.

Stelmach makes the same arguments he made in an advertisement last week in the Washington Post — that Alberta is a secure and stable source of oil, with "mandatory greenhouse gas reporting requirements."

"It is important ... that the process rely on factual information and be in keeping with the free trade principles that have served our energy relationship so well over the past quarter century," Stelmach wrote.

The pipeline, which would take Canadian crude oil from Hardisty, Alta., to Texas, needs a presidential permit issued by the State Department to go ahead.

The proposal has recently come under heavy criticism from U.S. politicians and environmentalists, who object to both the impact on the environment and how it would boost U.S. consumption of crude from the Alberta oilsands.

U.S. politicians also write Clinton

In his letter, Stelmach called comments that the oilsands have a higher "lifecycle" carbon intensity than conventional crude "a mistaken belief."

"In fact, the carbon intensity of conventional crudes tends to be on the increase while technological developments in the oilsands have reduced average carbon intensity by 39 per cent between 1990 and 2008."

Fifty members of the U.S. House of Representatives sent a letter to Clinton last month, urging the Obama administration to do a full assessment of the environmental impacts of the oilsands before allowing the Keystone expansion to go ahead.

Henry Waxman, the high profile congressman who chairs the House of Representative's Energy and Commerce committee, came out publicly against the project this week.

Last week, the Alberta government spent $55,800 to place the ad in the Washington Post to counter these criticisms, after the newspaper rejected Stelmach's letter for its op-ed page.

Premier Ed Stelmach's letter to U.S. Secretary of State Hillary Clinton

With files from The Canadian Press