There's a growing debate about whether the United States should start exporting some of its natural gas wealth. After all, America is currently awash in cheap gas, thanks to advances in shale drilling. And natural gas prices are high in other countries. So why don't we just ship some of our supply overseas for a tidy profit?

A Russian tanker carrying liquefied natural gas arrives in Japan. U.S. policymakers are currently debating whether we should get in on this action. (Tsuyosi Matsumoto -- AP)

Policymakers have been arguing over the pros and cons all year. Exporting more natural gas could boost the U.S. economy. But it might also lift the price of natural gas here at home, which could mean slightly higher electricity bills for Americans. (Since the Department of Energy would need to approve new export terminals, that means politicians get to weigh in.)

Yet there's one oft-overlooked aspect of this debate that could make all the bickering moot. It's still entirely possible that U.S. energy companies won't find it economical to ship all that much natural gas overseas in the near future. If so, that would mean natural gas exports could become a relative non-issue, regardless of what members of Congress think.

That was one interesting takeaway from a big new report by the Department of Energy, released on Wednesday. The report found that natural gas exports could, in theory, boost the U.S. economy by up to $47 billion in 2020. Those gains would likely outweigh the costs from higher domestic energy prices. Yet the report also suggested that large-scale exports might not materialize at all.

One reason is cost. Natural gas is relatively easy to transport by pipeline across land. But it's not quite as simple to ship overseas. The methane has to be liquefied first, chilled to -260°F so that its volume shrinks and it can be transported in giant ocean tankers. This technology is already widespread. But it can be quite pricey. Natural gas that sells for $3.70 per million BTU in the United States can cost $10 or $11 per million BTU once it's liquefied and transported abroad.

Now, exports might still be worthwhile even at that higher cost — after all, natural gas prices in Japan are currently around $17 per million BTU. That looks like an obvious trade opportunity. But a lot depends on how the global market develops in the coming years. If America's natural gas ends up being less plentiful than assumed, or if, say, countries in Eastern Europe start exploiting their own shale gas supplies, then U.S. exports will look less appealing.

Indeed, as Michael Levi points out, the Energy Department's baseline projection right now is that U.S. gas exports won't grow at all, given the current outlook for global demand. For truly large-scale exports to emerge, a number of things would have to fall into place — U.S. prices would have to stay low, while Japan would need to shut down its nuclear program entirely and bolster its appetite for natural gas. (If, for some reason, South Korea shut down its nuclear program, that could boost demand further.)

It's still unclear how all these factors will play out. Charles Ebinger of the Brookings Institution recently took a look (pdf) at different ways the global market for natural gas could unfold in the future. China and India might want to import more U.S. natural gas in the coming decades — or they might start developing their own shale-gas resources. Europe might seek out alternatives to Russian natural gas — or they might not. Canada and Australia could crowd the market with their own gas supplies. There are a lot of variables.

Still, despite the uncertainty, gas exports are becoming a higher-profile issue. U.S. gas companies are already lining up to ink long-term contracts with buyers abroad. And at least seven new export terminals are awaiting approval. (Back in January, the Department of Energy approved Cheniere Energy’s Sabine Pass Liquefaction terminal in Cameron Parish, La., which could ship up to 2 billion cubic feet of gas per day by 2015.)

For now, the Energy Department report is a sign that the Obama administration may end up looking favorably on exports, even though some members of Congress, like Sen. Ron Wyden (D-Ore.) are still skeptical. But there are still questions about how the market will actually shape up.

Further reading:

-- An overview of the debate in Congress over natural gas exports.

-- Michael Levi has a detailed breakdown of the latest Department of Energy report on exports. He's also written his own report on the topic. Both are recommended.