The companies proposing to build the $16.2-billion Mackenzie Gas pipeline again delayed its proposed startup date on Monday.

The leader of the consortium behind the long-delayed project — Calgary-based Imperial Oil Ltd. — said natural gas could start flowing from the Beaufort Sea in 2018 at the earliest.

The 1,200-kilometre natural gas pipeline would be built through the Northwest Territories' Mackenzie Valley. (CBC)

The consortium has yet to make its final decision on whether to go ahead. Imperial said in a letter to the National Energy Board that the companies would likely make their decision on whether to proceed in late 2013.

The update included a market analysis that suggested there will be a long-term need for Arctic gas, despite new technology that has opened up previously inaccessible shale formations in the south.

When the companies filed their application in 2004, the start date was 2009. Several delays have been announced since then, while the companies have awaited clearance from regulatory agencies. The panel reviewing the project's environmental and social effects conditionally approved it on Dec. 30, 2009, and the National Energy Board issued draft conditions for its approval earlier this month.

There is no update to the Mackenzie project's most recent cost estimate of $16.2 billion, established in 2007.

The 1,200-kilometre pipeline would carry up to 1.2 billion cubic feet of gas a day to markets in southern Canada and the U.S.

The other companies in the consortium are Royal Dutch Shell Plc, ConocoPhillips, Exxon Mobil Corp and the Aboriginal Pipeline Group.

With files from The Canadian Press