TIMELINE-Enbridge's Northern Gateway oil pipeline proposal

April 21 (Reuters) - Here are some key dates in Enbridge Inc's bid to build a 525,000-barrel-per-day pipeline from the Alberta oil sands hub of Edmonton to Kitimat, British Columbia, on Canada's Pacific Coast. The proposed C$7.9 billion ($7.17 billion) project has run into fierce opposition from aboriginal communities and environmental groups, and cost estimates have more than doubled since it was first announced. The Canadian government is expected to make its final decision on the project in mid-June.

March 6, 2002 - Enbridge says it is sketching out plans for a pipeline from northeastern Alberta to Canada's West Coast.

April 14, 2005 - Enbridge and PetroChina Co sign a deal to cooperate on a C$2.5 billion pipeline to transport 400,000 bpd from Alberta to the West Coast.

July 15, 2005 - Enbridge says it has started engineering and environmental field studies for the Gateway pipeline project.

Oct 3, 2005 - Support from shippers prompts Enbridge to boost the size of an adjacent condensate line for Gateway to 20 inches from 16 inches (51 cm from 41 cm), allowing more than 150,000 barrels a day of condensate to flow eastward to Alberta.

Oct 14, 2005 - Enbridge picks Kitimat, British Columbia, as the end point for the pipeline because of its deepwater port.

June 27, 2006 - The head of Enbridge's Gateway project dismisses fears that objections from aboriginal groups will delay the pipeline, expects to have it in operation by 2010.

Nov 1, 2006 - Enbridge delays Gateway in favor of accelerating new lines to U.S. markets.

Feb 21, 2008 - Demand from producers and refiners prompts Enbridge to rekindle Gateway, now estimated to cost C$4 billion and ship 525,000 bpd.

Oct 6, 2009 - Enbridge says it expects project costs to rise.

March 23, 2010 - Aboriginal groups on the Pacific Coast vow to block the pipeline, now expected to cost $5.5 billion, saying the environmental danger of oil tankers traveling through coastal waters is too great.

May 27, 2010 - Enbridge files Northern Gateway pipeline proposal with the National Energy Board.

Jan 20, 2011 - Enbridge says China's Sinopec Corp among a consortium of producers and refiners that has provided about C$100 million to fund the line's regulatory and development costs.

Aug 24, 2011 - Enbridge and shippers agree on Northern Gateway terms.

Sept 22, 2011 - Northern Gateway critics are given more time to comment on Enbridge proposals.

Dec 2, 2011 - Gitxsan First Nation becomes first aboriginal partner for Northern Gateway project.

Jan 4, 2012 - Suncor Energy Inc, Cenovus Energy Inc , MEG Energy Corp, Nexen Inc and Total SA identified as backers for Northern Gateway.

Jan 9, 2012 - Natural Resources Minister Joe Oliver describes Northern Gateway pipeline opponents as foreign-funded radical groups.

Jan 10, 2012 - Joint review panel hearings into Northern Gateway project open in Kitimat.

Jan 18, 2012 - Enbridge deal with Gitxsan First Nation collapses.

Feb 10, 2012 - Canadian Prime Minister Stephen Harper says the government is committed to ensuring Canada has necessary infrastructure to move energy resources to markets.

June 5, 2012 - Enbridge says 60 percent of aboriginal communities living along the Northern Gateway route have agreed to accept an equity stake in project.

July 20, 2012 - Enbridge pledges new safety measures that will add as much as C$500 million to cost of project.

July 23, 2012 - British Columbia government says needs more benefits from new pipelines, sets out minimum conditions for approval.

Sept 26, 2012 - Environmental groups sue Canada over Northern Gateway route.

April 12, 2013 - Joint review panel issues draft conditions for Northern Gateway.

May 31, 2013 - Government of British Columbia rejects Northern Gateway project on grounds the company has not spelled out oil spill response plans.

Nov 5, 2013 - Alberta and British Columbia announce framework agreement that could clear path for new pipeline development to the West Coast.

Dec 19, 2013 - The National Energy Board releases its Northern Gateway decision.

Jan 17, 2014 - A coalition of environmental groups launches a legal challenge to the federal review panel recommendation in favor of the Northern Gateway pipeline.

Jan 17, 2014 - British Columbia's Haisla and Gitxaala Nations file court challenges to the federal review panel recommendation in favor of the Northern Gateway pipeline.

Jan 22, 2014 - British Columbia's Gitga'at First Nation files a court challenge to the federal review panel recommendation in favor of the Northern Gateway pipeline.

Apr 12, 2014 - Residents of Kitimat, where the pipeline's marine terminal would be built, vote against Northern Gateway in a non-binding plebiscite. More than 60 percent of eligible voters turn out, with 58.4 percent voting "no" and 41.6 percent voting "yes." ($1=$1.07 Canadian)

(Reporting by Nia Williams and Julie Gordon; Editing by Peter Galloway and Douglas Royalty)