nytimes.com – Photo Q. What is the Keystone XL pipeline? A. The Keystone oil pipeline system is designed to carry up to 830,000 barrels of petroleum per day from the oil sands of boreal forests in western Canada to oil refineries and ports on the Gulf Coast. About half of the system is already built, including a pipeline that runs east from Alberta and south through North Dakota, South Dakota and Nebraska. The State Department is now reviewing a proposed 1,179-mile addition to the pipeline, the Keystone XL, a shortcut that would start in Hardisty, Alberta, and diagonally bisect Montana, South Dakota and Nebraska.