PORTLAND — Portland city officials and environmental advocates held a news conference at City Hall Wednesday morning to support a proposal to prohibit the purchase of tar sands oil for city operations.

The Portland City Council will vote on Wednesday night on the proposal, which is modeled after pledges made by 18 major corporations concerned about tar sands oil. If approved, the city would not purchase refined tar sands oil for their heating fuel and other operations.

Additional Photos

Portland Mayor Michael Brennan, center, joins Emily Figdor, left, of Enviroment Maine, Eliot Stanley of the Sebago Lake Anglers Association and City Councilor David Marshall, right, at a news conference at Portland City Hall to endorse a tar sands-free Portland to be voted on by the city council on Wednesday. John Patriquin / Staff Photographer

The issue has gained attention because oil companies want to use a 62-year-old pipeline that passes next to Sebago Lake to carry tar sands oil from Canada to Casco Bay, where it would be loaded onto tankers for export, according to Emily Figdor, executive director of Environment Maine. Pipelines carrying tar sands oil, which is more corrosive, heavier and thicker than conventional crude, are believed by critics to be more prone to spills, and spills of the crude are especially difficult to clean up because the heavy oil tends to sink in water.

The council also is sure to hear opposition to the proposal Wednesday evening.

John Quinn, executive director of the New England Petroleum Council in Boston, called criticisms of tar sands inaccurate and misleading in a column earlier this week in the Portland Press Herald. Quinn wrote that there is no evidence the tar sands oil is more corrosive than other crude oils.

Figdor and Portland Mayor Michael Brennan were among the supporters speaking out at City Hall this morning.

The council is considering the issue just before what is expected to be the biggest tar sands protest held to date in the region. Environmental advocates predict hundreds of people from across New England will gather for a march and rally Saturday in downtown Portland to demonstrate opposition to the proposal to send tar sands oil through the 236-mile long, 62-year-old Exxon/Enbridge pipeline across Canada, Maine and the Northeast.

“Maine and the region have everything to lose and nothing to gain from sending toxic tar sands across our state,” said Emmie Theberge of the Natural Resources Council of Maine, who is helping to organize the rally, along with other groups inclduing 350 Maine and Environment Maine.

“Hundreds of people will descend on Portland Saturday to make a point: We cannot afford the risk of  tar sands oil surging across the Northeast in Exxon’s pipeline and will be calling on the State Department to demand an environmental review of this risky proposal. There is too much at stake.”