Locked up inside the 6 million years of sediment that makes up the Green River Formation, which extends across mostly public lands in Colorado and Utah, may be the equivalent of a few trillion barrels of oil. Even if only half of it is recoverable, the oil shale of the Mountain West could one day fuel the world, turning the phrase "U.S. energy independence" from slogan to reality.
Provided, that is, that there's a reasonable way to coax the fuel out of the rock.
Trapped in fossil-fuel purgatory, oil shale has to be heated to super-high temperatures, a process called "retorting" that requires enormous amounts of water. No one can even say for sure how much, although some energy companies try.
Utah-based Red Leaf claims its technology needs only a tiny amount; other estimates say that full-scale development of oil shale in Colorado would require more water than all of Denver uses in a year.
"There's been a great deal of speculation on water needs for oil shale, but it's all based on unproven technology," says Steven Hall, Colorado spokesman for the Bureau of Land Management, which recently signed a lease with ExxonMobil for an experimental oil shale project in the Piceance Basin.
"I don't think the technologies those (low) water-use estimates are based on are commercially or environmentally feasible," Hall said.
In November, the BLM published a fresh analysis of oil shale development's environmental impacts on Western public lands. Much of the analysis, which also looks at tar sands in Utah, is concerned with water - the lack of it in this arid region, the great need any energy-extraction technique has for it, and the vulnerability of freshwater aquifers to industrial contamination.
As a consequence of this and other concerns, the analysis proposes reducing the 2 million-plus acres of public lands opened to commercial lease in 2008 to just under 700,000 acres limited to research projects.
Lawmakers including Sen. Orrin Hatch, R-Utah, warn that the BLM's parent, the U.S. Department of Interior, stands in the way of economic progress. But not even the oil producers have figured out how to get the water to the rock without incurring huge energy costs - costs that may not pencil out in the final analysis.
In other words, it may take more energy to get the water to the oil shale than anyone can actually extract from it.
This problem with the so-far embryonic industry is what regulators and industry experts call an "energy-water nexus" issue: Just as water needs energy to travel from source to tap, nearly every form of energy needs water throughout its lifecycle, from mining to generation to reclamation.
Most of the country's electricity, for example, comes from coal, gas or nuclear plants that heat water until it flashes to steam and spins a turbine; that steam then has to be cooled back into water - using yet more water.
Biofuels use water, from cultivation to distillation, and some forms of geothermal production consume as much as 800 gallons per megawatt-hour of electricity, the amount of power the average home uses in a month.
Energy, says the Congressional Research Service, outpaces municipal use in its water demands; it's second only to agriculture. And while farms and cities have begun to conserve water, energy - thanks to biofuels and shale gas - is increasingly voracious.
Nor is consumption the only issue: Electricity plants return almost all that cooling water to the source, but they return it at a higher temperature, altering riparian or marine ecosystems.
The Government Accountability Office has published five reports over the last three years on energy-water nexus issues, analyzing oil shale's water needs, the interdependency between electrical plants and their water supplies, and the hydrologic impacts of hydraulic fracturing.
But the GAO's sixth and latest report, published in September, argues that the most crucial component of the nexus is information sharing - between state and local governments, industry and science, and even across federal agencies.
"People have been aware of these issues from their individual viewpoints at various agencies," says Frank Rusco, the GAO's director of water and energy issues.
The Energy Department might understand that hydrofracturing for natural gas could contaminate local water supplies, for instance, but the Environmental Protection Agency may lack baseline studies showing the water's condition before industry got there.
Interior officials might suspect that developing oil shale in Colorado could exhaust local water supplies, but not have accurate data to prove it.
In 2003, the U.S. Geological Survey told GAO investigators that it had not shared data on freshwater supplies with other federal agencies in more than three years - not that anyone had asked.
The Energy Policy Act of 2005 "highlighted the need for agencies to do more coordinating and think in a more strategic way ... about energy and water policy issues," Rusco says, so Congress directed the Energy Department to set up an agency devoted to the energy-water nexus.
Yet while some coordination has begun - the Environmental Protection Agency and the Energy Department, for instance, have initiated a program to protect groundwater from energy development - a dedicated energy-water agency still exists only on paper.
"Agencies have competing agendas," Rusco said. "Coordinating strategies across several agencies is a difficult thing to accomplish."
It's also expensive: Rep. Eddie Bernice Johnson, D-Texas, who commissioned the latest GAO report, has authored two bills that would promote agency coordination when energy affects water and vice versa, one calling for $300 million to fund the effort.
Neither is likely to pass in the deficit-obsessed Congress, for which tasks such as monitoring the country's supply of freshwater seems to be a luxury.
Last fall, House Natural Resources Subcommittee Chairman Doug Lamborn, R-Colorado Springs, asked USGS Director Marcia McNutt why the agency supports energy program cuts but asks for increases in climate change research funding. He then read her a list of current gas prices.
Congress is unlikely, then, to allocate the funds needed for USGS to maintain its vast nationwide network of stream gauges, no matter how much better data on water, climate and drought might matter to the future of unconventional oil and gas.
"People may not fully grasp the scale of the increase in energy development," Rusco says, especially when it comes to thirsty processes like hydraulic fracturing and oil shale.
"The intensity of it and the amount of water it uses is unprecedented." And, unfortunately, still somewhat unknown.