The rationale for Keystone was a way to bring together booming US oil production, and to a lesser extent, production from the oil sands in Northern Alberta, to Gulf Coast refineries that were facing declining imports from Mexico and Venezuela. The project was first proposed in 2008 and was supposed to begin carrying 830,000 barrels a day in 2012.
But the market didn't wait for the pipeline to be built, and landlocked Canadian crude has found its way to Texas and Louisiana refineries by rail instead. Canadian oil exports by rail tripled to a record 182,000 barrels a day in the third quarter, according to Canada's National Energy Board. The United States has also been importing Canadian oil like gangbusters, showing that the trade will happen with or without the pipeline extension (Keystone XL is an addition to the existing pipeline). Data from the US Energy Department showed US imports of Canadian crude reached a record 3.1 million barrels a day in September.
...
So with some of the project's goals already being met, in terms of increased production flowing from Canada to the US, the question has become, why is a pipeline needed anymore? And now, with the oil price down more than 50 percent since June, Canadian production is certain to fall, lessening demand for oil transportation and thus casting doubt on the economics of the project according to observers.