EMMA ALBERICI, PRESENTER: The Queensland Government wants to open up what could become one of the world's largest coal regions, the Galilee Basin.

Tonight there are new questions about the financial viability of one of the big players in the project, Indian coal conglomerate Adani.

There are two other key investors, a Gina Rinehart joint venture with another Indian giant, GVK, and Waratah, a company owned by Clive Palmer.

Now a Greenpeace-commissioned investigation has found Adani is carrying $12 billion of debt and needs billions more to develop the project, just as the world coal market is looking grim.

The ABC's environment reporter, Jake Sturmer.

JAKE STURMER, REPORTER: It's a beautiful spring day in the heart of Brisbane. There are smiles and optimism at the annual Galilee Basin Coal and Energy Conference.

MICHAEL ROCHE, CEO, QUEENSLAND RESOURCES COUNCIL: Each year that one of these conferences are held, we are edging closer to a project in the Galilee Basin.

JAKE STURMER: The Galilee Basin is a remote but massive coal deposit in the heart of Queensland with equally huge economic potential. As yet, it's an untapped resource, and green groups want to keep it that way.

There's so much contention surrounding the developments, this is all one of the major players, GVK, wanted you to see from their presentation at the Brisbane conference.

There are three major players in the Galilee. GVK-Hancock, a joint venture between Gina Rinehart's Hancock Coal and Indian conglomerate GVK; Waratah, a company owned by Clive Palmer, and Adani, run by Indian billionaire Gautam Adani.

Far from the blue skies of Brisbane, Sydney financial analyst Tim Buckley sees storms on the horizon for Adani. He's been commissioned by Greenpeace to conduct a financial investigation of the Adani Group.

TIM BUCKLEY, RESOURCES ANALYST, ARKX INVESTMENT MGMT: They are betting the entire company on their Australian foray into opening up the Galilee.

JAKE STURMER: The analysis flags significant problems for Adani. The document claims the Galilee project's uncommercial because of the low coal price and the report says the Adani Group has worrying levels of debt.

TIM BUCKLEY: We estimate the external debt of the Adani Group at US$12 billion. So it is a very financially leveraged group of companies. And that's before funding the majority of the $10 billion to be invested in Australia.

JAKE STURMER: Tim Buckley says Adani is too much of a gamble.

TIM BUCKLEY: Their core business isn't making money, and therefore, they're not actually able to cover the interest costs, so debt, when you can't cover the interest, is a problem.

JAKE STURMER: In a statement, Adani said it had complete confidence in the viability of its projects and criticised the motivations of the report as "short-sighted", ignoring the "long-term fundamentals".

MICHAEL ROCHE: It's very nice for Greenpeace to be concerned about the coal businesses, the economics of the coal market, but I'd never rely on Greenpeace to make a call on whether it's a good time or not a good time to be investing in a new coal mine.

JAKE STURMER: But it's not just green groups ringing alarm bells. Many resources analysts agree the numbers just don't stack up for coal, at least in the short term.

What do you see for the future?

MATTHEW TRIVETT, RESOURCES ANALYST, PATERSONS SECURITIES: I think in the thermal market it's going to be quite difficult to see a lot of these greenfield or peripheral basins coming online.

JAKE STURMER: But it's not all doom and gloom. GVK-Hancock has made progress on plans for a rail link to the remote basin, which is 90 kilometres from the nearest sealed road. They've signed a non-binding deal with rail company Aurizon.

Rail lines to get the coal to port are one thing; digging it up out of the ground is another. To encourage that, the Queensland Government has promised financial incentives to help make these massive projects happen.

JEFF SEENEY, QUEENSLAND DEPUTY PREMIER: The low price at the moment is certainly making it difficult and causing people to - causing everyone to be a little hesitant. But it's the price over the next 20 or 30 years that will determine whether or not the Galilee Basin is viable.

JAKE STURMER: But crucial decisions about the Galilee will need to be made in a much shorter timeframe.

Jake Sturmer, Lateline.