Battle Over Keystone XL Pipeline

Nebraska's Supreme Court ruled against a challenge to the Keystone XL oil pipeline's route through the state on Friday, clearing the way for the Republican-controlled U.S. Congress to try to force President Barack Obama to approve the project.

The 1,179-mile (1,900-km) pipeline would send up to 830,000 barrels per day of oil sands crude from Hardisty, Alberta, across the U.S. border to Steele City, Nebraska, where it would connect with the project's already-built Gulf Coast leg.

Following are key dates in the six-year history of the project:

July 2008 - TransCanada Corp announces plans to expand its existing 590,000 bpd Keystone oil pipeline system to the Gulf Coast.

September 2008 - TransCanada Corp files an application with the U.S. State Department for a presidential permit allowing construction of the project.

August 2011 - The State Department issues its final environmental impact statement for the project. It finds Keystone XL will not have significant adverse effects on the environment and begins a 90-day comment period to determine if the project is in the U.S. national interest. November 2011 - State Department says it needs to assess alternative routes for the pipeline in Nebraska to avoid the environmentally sensitive Sandhills region. TransCanada reaches an agreement with Nebraska's Department of Environmental Quality to find an new route. December 2011 - The U.S. Congress attaches a provision to a tax cut bill requiring Keystone XL to receive its permit within 60 days unless President Obama determines that the project is not in America's national interest.

January 2012 - Obama declines to issue the permit, saying the deadline does not allow sufficient time to assess the line's new route through Nebraska. TransCanada says it will reapply. February 2012 - TransCanada says it will start building Keystone XL's $2.3 billion southern leg from Cushing, Oklahoma, to the Gulf. The project, dubbed the Gulf Coast line, is not subject to federal review.

May 2012 - TransCanada applies again to the State Department for a presidential permit for the project after coming up with a new route through Nebraska. January 2013 - Nebraska Governor Dave Heineman approves the new route.

March 2013 - The State Department issues its review of the revamped application, saying the pipeline would not increase greenhouse-gas emissions and would have few environmental impacts along its route. August 2013 - TransCanada says it will build the $10.11 billion (C$12 billion) Energy East line to take 1.1 million barrels per day of Western Canadian crude to refineries and ports in Quebec and New Brunswick. January 2014 - Keystone XL's southern leg begins shipping oil from Cushing to Texas. The State Department issues its final environmental review of the revamped application. It repeats its March 2013 position. February 2014 - A Nebraska court invalidates the governor's decision to allow the Keystone XL pipeline to pass through the state. It rules the law passed by the state's legislature, which gave Heineman the decision on the route instead of the Nebraska Public Service Commission, was "unconstitutional" and "void." Heineman appeals the decision.

April 2014 - The Obama administration says it will delay a decision until at least November, until the Nebraska Supreme Court settles the dispute over Keystone XL's path. September 2014 - TransCanada re-applies for a permit for the line's route through South Dakota after its original approvals expire. October 2014 - TransCanada files for Canadian regulatory approval for the Energy East pipeline project. November 2014 - Republicans make big gains in the mid-term elections, giving them majorities in the House of Representatives and the Senate. They put forward a bill to force Obama to approve the project. Approved by the House, the bill fails in the Senate.

TransCanada revises its cost estimate for the project, boosting the expected price tag to $8 billion from its prior $5.4 billion estimate.

January 2015 - Republicans put forward a new bill to force approval of the project. It passes in the House, hours after the Nebraska Supreme Court approves Keystone XL's route within the state. A Senate vote is still awaited.

(Reporting by Scott Haggett in Calgary, Alberta; Editing by Tom Brown)

($1 = 1.1867 Canadian dollars)