America's oil boom is no longer a secret. But the impact it will have on the economy still isn't clear. Low gas prices haven't arrived. A manufacturing boom remains elusive.

But there's one area we can measure the impact of our energy boom with precision: The trade deficit. And the numbers are staggering.

Let's take a look.

America became a consistent net exporter of finished petroleum products in 2011 for the first time in half a century:

Petprod

Source: Energy Information Agency.

Now, this only represents finished petroleum products like gasoline and diesel. Foreign countries like Mexico have a voracious appetite for our finished petroleum given their lack of refinery capacity. America still imports crude oil. But our reliance on oil imports is shrinking fast, nearing the lowest level in two decades:

Crudeimp

Source: Energy Information Agency.

In June, 2008 America imported some 300 million barrels of crude. In June of this year, that figure was a quarter lower, at 231 million barrels. That's simply huge. 

Put our dwindling reliance of imported oil together with a booming export market for finished petroleum products, and you get a remarkable statistic: U.S. net imports of crude and petroleum products are back to where they were nearly 30 years ago:

Netimp

Source: Energy Information Agency.

In June 2008 America imported a net 11.2 million barrels of crude and petroleum products per day; this June, it was down to 6.2 million barrels. That's a difference of five million barrels per day, or 1.8 billion barrels per year.

Slap a dollar amount on that figure, and you're talking real money. Energy analyst Daniel Yergin wrote last year:

The increase in domestic oil production over the past five years will reduce our oil-import bill this year by about $75 billion. The growth of shale gas will save the U.S. from spending $100 billion a year on imported [liquefied natural gas], which was the likely prospect five years ago.

$175 billion per year. And that was last year. The savings is almost certainly more this year, with lower crude imports and higher finished-product exports.

The end result: An oil boom equals a smaller trade deficit. The economy's overall trade deficit -- the amount our imports exceed exports -- has fallen by half since 2008, to 3% of GDP from nearly 6%:

Tradedef

Bureau of Economic Research.

A decade ago, Warren Buffett worried about our growing trade deficit and told Fortune magazine:

In effect, our country has been behaving like an extraordinarily rich family that possesses an immense farm. In order to consume 4% more than we produce--that's the trade deficit--we have, day by day, been both selling pieces of the farm and increasing the mortgage on what we still own.

We're still selling off the farm, but much less than before, and much less than nearly anyone expected just a few years ago.

Analysts trying to figure out how to benefit from America's energy boom tend to zero in on specific companies. Cheniere Energy (NYSE: LNG) has an opportunity in liquefied natural gas exports, Devon (NYSE:DVN) in fracking. But the biggest beneficiary may be the economy at large -- you, me, everyone. We now live in an economy less reliant on strangers for energy than we have in over a decade. There is a rebuttal to rejoicing over this; some say imported oil is our friend. But as Buffett worried a decade ago, an ever-expanding trade deficit meant "we have entered the world of negative compounding -- goodbye pleasure, hello pain." That pain is quickly turning into a pinch. 

Fool contributor Morgan Housel has no position in any stocks mentioned. The Motley Fool owns shares of Devon Energy. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.