SCOTT Stevens of Advanced Resources International gave an interesting talk at a Hong Kong conference this week on the future for shale gas supplies. This is one of the most interesting (and encouraging) developments of the last few years for the US economy; a plentiful source of cheap energy. At other times, I have pointed out one of the disturbing themes of the recent crisis; that recession in the developed world has not been accompanied by falling commodity prices, as it has in the past. Thanks to Asian demand, the developed world is now a price-taker not a price-setter. More speculatively, I have suggested that the greater cost of extracting energy (particularly oil) is a problem for global growth, which since 1800 has been powered by cheap carbon fuels; the amount of energy output we get for each energy input has been declining. If the world was a corporation, that would be a squeeze on profit margins.

Mr Stevens pointed out that the sudden emergence of shale has had forced the US price down from $30 to $2.80, below the marginal cost of production, which he estimated at $4-$5. Supplies may last for more than 100 years. Shale oil may also be useful but not on the same scale - perhaps another 2m barrels a day by 2020.

But the US has been exceptionally good at exploiting its supplies and has more favourable geology than other countries. As readers may know, fracking involves drilling down and then across. Many US fields are structured like a wedding cake, with the shale arranged in a neat horizontal layer; that makes it easy to get at the gas. But Mr Stevens says that European and Asian fields have more faults; the various layers have slipped so they are not parallel. The drill may hit shale for a while, but then it will be confronted with a different type of rock.

Secondly, the US has lots of private land and open geological records; it is easy to know where the shale might be and easy to persuade a farmer to grant access to a field in return for a stream of loyalties. In other countries, land is public and, in China, the geology is treated as a state secret. It is thus harder for private companies to explore. Thirdly, the US has a lot of small independent energy companies that are used to taking a punt on this kind of project; other countries lack the same structure, and the big majors are not as inclined to take risks. Fourth, the US has a highly competitive energy supply industry that helps to keep costs down.

As a result, Mr Stevens thinks the scope for other countries to enjoy the same shale boom are limited; Argentina might manage it, as might Mexico. Australia has good geology. But Europe and Asia may struggle.