How in the world can we figure out just how much oil and gas is hidden within the rocks of this planet? For the moment, we’re still at the wild guessing stage, as a new report commissioned by the US Energy Information Administration makes clear.

The study, updating one from two years ago, expanded from 32 countries to 41, from 48 basins to 95 and from 69 formations to 137. Yet its estimate for the total technically recoverable reserves of shale natural gas increased by a notably less ambitious 10 percent to 7,299 trillion cubic feet,  amounting to 65 years’ of supply at the current consumption rate. Tight oil checked in at a relatively scarce 345 billion barrels, a mere decade’s worth of guzzling at the current rate.

That means estimates will continue to get refined as more rocks are drilled. The geology of shale is highly variable, so that any given well will only tell you about the oil and gas in spots it intersects and not all that much about the neighboring acre, much less the neighboring state. For example, only 1 percent of the booming Marcellus shale in Northeastern US has been tested by production so far, according to the study. Decades might pass before we really know how much gas it contains, based on the pace of current extraction.

But those will likely be decades of increasingly aggressive shale exploitation overseas, so let’s look at the current best guess about where all that oil and gas is hiding.  Overall shale contains 9 percent of the world’s technically recoverable crude oil reserves and 32 percent of natural gas, the study estimates. The bulk of those reserves is located in just a few countries, reflecting the lack of exploration elsewhere more so than any natural advantage.

Russia leads the world in estimated reserves of shale oil with 75 billion barrels, or 22 percent of the total, followed by the US with 58 billion, China (32 billion), Argentina (27 billion) and then Venezuela and Mexico with 13 billion apiece.  The thing to note about this list is that the US is the only country on it where private prospecting has a long and rich tradition. In China and Russia, state-sponsored national champions have a stranglehold on the process. And Argentina, Venezuela and Mexico remain difficult places to do business.

When it comes to reserves of shale natural gas, China is tops with 1,115 trillion cubic feet (tcf), or 15 percent of the estimated global total. Next is Argentina with 802 tcf, Algeria (707), US (665), Canada (573), Mexico (545) and Australia with 437 tcf. Here, the prospecting prospects are improved by the available opportunities in the US, Canada and Australia, all business-friendly countries.

The main takeaway is that we still don’t know how much mineral wealth is buried within all the rocks and won’t until we drill them. But the US is only the first country to be transformed by shale drilling, not the last. And based on the numbers this study has unearthed there’s a lot of hard work ahead in some pretty challenging jurisdictions.