The pipeline stretches 2,687 miles across Canada and the US and it is used to deliver oil from Alberta to Houston and Patoka - in the states of Texas and Illinois, respectively.
The original Keystone Pipeline (Phase 1) began operation in 2010 and runs from Hardisty, Alberta, through Manitoba and North Dakota, to Steele City, Nebraska.
Phase 2 extended the system south from Nebraska to Cushing, Oklahoma.
Phase 3, also known as the Gulf Coast Pipeline, connects Cushing to refineries in Port Arthur and Houston, Texas, and went online in 2014.
