Almost any form of producing and transporting oil risks an environmental disaster if things go wrong, as was demonstrated in the summer of 2010 by the major British Petroleum spill in the Gulf of Mexico.  Historically however land-based Pipelines have been far safer than Oil Freighters or off-shore platforms because of the ease of access, which means that spills can usually be responded to rapidly. The real damage with the BP Spill was due to its isolated location in deep water and the consequent difficulty of reaching it.  Furthermore, fears of the carbon emissions are flawed because they are based on the assumption that if the Pipeline is not approved the Tar Sands will not be developed. But this is not the case. The Canadian Government has already shown interested in an alternative Chinese proposal which would see a Pipeline built to deliver the oil to the Pacific, and eventually to the Chinese market. [1] If the oil is going to be burned one way or another, it is best for the United States to do it, because the United States enjoys higher fuel efficiency standards and generally cleaner vehicles.  [1] Yahoo news, 2012,