The main backer of a drawn-out proposal for a $16-billion natural gas pipeline down the Mackenzie Valley has reached a tentative deal with a holdout aboriginal group over land access.

"We have an agreement that's being brought to the communities," Ria Letcher, executive director of the Dehcho First Nation, said Monday. "If they're OK with it, we have an agreement.

"It's about access to land and benefits arising from access to land."

The Dehcho claim traditional lands in the southwest corner of the Northwest Territories that would be part of the right of way for the Imperial Oil pipeline.

The claim covers about 40 per cent of the pipeline's projected route. The Dehcho are the only remaining First Nation along the route that hasn't expressed support for it.

Letcher said the tentative deal doesn't mean the Dehcho are ready to join the Aboriginal Pipeline Group, a consortium of First Nations that expects to control one-third ownership in the pipeline when -- and if -- it gets built.

Two Dehcho communities have already broken with their leadership over membership in the consortium. Fort Simpson and Fort Liard have both voted to join the ownership group.

But Letcher pointed out that the majority of community members "haven't signed on this."

Negotiators will spend the next week visiting Dehcho communities to prepare for ratification votes. Those votes will be discussed next week at a Dehcho leadership convention in Fort Simpson, N.W.T.

Last month, Environment Minister Jim Prentice said the government has offered an undisclosed amount for infrastructure and pre-construction costs, as well as a sharing of risks and returns.

Such positive developments have been rare for the 1,200-kilometre pipeline, which would carry natural gas from the coast of the Beaufort Sea south to the Alberta boundary, where it would connect into TransCanada Corp.'s (TSX:TRP) existing network.

The proposal has been stalled for years in regulatory hearings.

A panel assessing the proposal's social and environmental impact was supposed to have reported by now, but that isn't expected to happen until the end of the year.