The 2,735km (1,700-mile) oil TransCanada pipeline would link the oils sands fields of northern Alberta to Texas refineries and aims to begin operating in 2013.

The environmental risks include: strip-mining huge chunks of Alberta's boreal forest, using vast quantities of water and energy, creating 82 percent more emission than those from conventional crude oil, toxic holding ponds that kill migrating birds and pollute downstream watersheds, increased risks of pipeline leaks oil sands oil in a pipeline is more corrosive than crude oil, disruption of the porous sandy soils of the Montana and the Nebraska Sand Hills, and risks to the Ogallala Aquifer, which provides drinking water for two million people.

The US Environmental Protection Agency gave the State Departments draft environmental impact statement for the Keystone XL pipeline its lowest possible ranking: "inadequate" July 2010. Deficiencies cited included lack of accounting for greenhouse gas emissions, safety and spill-response planning concerns, and inattentiveness to potential impact on Canadas indigenous communities.

That criticism prompted preparation of whats known as a supplemental environmental impact statement on Keystone XL, expected spring 2011.

A coalition of 32 groups sent a letter to Secretary of State Hillary Clinton early in April asking her to extend the usual public comment period from 45 to 120 days and to organize on-the-ground public hearings in Montana, South Dakota, Nebraska, Kansas, Oklahoma and Texas.

Eleven US Senators, and fifty Members of the US House of Representatives have publicly opposed the Keystone XL.

On April 6, 2011 President Barack Obama said concerns about the potentially "destructive" nature of the Canadian "tar sands" need to be answered before his administration decides whether to approve the construction of Calgary-based TransCanada's controversial Keystone XL pipeline.