IT has been described as the 21st-century equivalent of the California gold rush.

America's embrace of so-called unconventional hydrocarbons has over the past few years made it the first country to become a major producer of shale gas and oil.

The country's petroleum reserves have soared, spurring talk that the US will no longer need to depend on the Middle East and may even be able to start exporting to the rest of the world. For the first time in eight years, countries in the Organisation for Economic Co-operation and Development (OECD) last year achieved a rise in crude oil production.

Gas prices in the US have also come down by about two-thirds, which has provided a big boost for the economy at a time when it might otherwise have been on its knees.

The American success has not gone unnoticed on this side of the Atlantic. Last week, the British Geological Survey (BGS) published its study into the potential for shale gas in the north of England. It reckons that the region might contain as much as 1300 trillion cubic feet of the stuff – a massive increase on its estimate from three years ago, coming on the back of more recent announcements about the area's potential from exploration licence holders Cuadrilla Resources and IGas Energy.

Although the BGS's figure is an order of magnitude more than will be extractable, it believes the reserves could last the country for 25 years. And that is before it gets around to properly surveying the deposits that exist in the rest of the country, including some in central Scotland.

Britain has gone from being a net exporter of gas at the turn of the century to now relying on imports for almost half of our requirement. As well as having to rely on the likes of Qatar and Nigeria, this is a serious drag on the country's trade figures and creates inflation.

Many experts believe that the UK quickly needs to build new gas-fired electricity plants to replace the coal-fired ones that are closing and to provide back-up when the wind turbines are not turning. If the UK is more heavily reliant on gas-fired power, goes the argument, it will be cheaper to get it out of our ground, even by unconventional means, than to get it from elsewhere.

There are several methods of exploiting unconventional hydrocarbons. One involves extracting coal-bed methane out of deep coal seams (gas is more traditionally found in more porous rock, such as sandstone).

Another method produces shale gas, which can require more laborious and controversial techniques such as hydraulic fracturing or "fracking", involving sending water and chemicals at high pressure several kilometres below the Earth's surface to fragment the rocks and allow the gas and oil to escape and be brought to the surface.

Fracking has raised serious concerns from environmentalists worried about potential pollution to the water table, and earthquakes. The procedure was the ''likely cause'' of earth tremors near Blackpool in 2011, a report found.

Despite those concerns, the UK Government has announced plans for everything from tax incentives to encourage shale gas production to payments for communities in the vicinity of fracking.

The big question is how long this filip will last. Not long, say some observers. For one thing, most shale gas production is no longer commercially viable because of the price drop. It generally depends on a price of about $5 (£3) per million cubic feet, rather higher than the current sub-$3.50 price.

This is said to be why the focus has switched much more to oil in the past couple of years, where the market is to a greater degree international and not so susceptible to events in one country. According to Statoil, which is producing shale oil in the Bakken area of North Dakota in the US, it needs a barrel price of about $60 – far below today's price of around $100.

However, some question how much oil is recoverable. According to a recent report by the Energy Policy Forum, reserves have been over-estimated by between 100% and 500%.

Jean Laherrere, one of the world's most influential petroleum watchers, blames a change to the US stock market reporting rules a few years ago that broadened what energy companies could include in their proven reserves statements, plus a flood of investment cash unleashed by the Federal Reserve's quantitative easing policy.

He says: "The numbers published of reserves of unconventional hydrocarbons are just pure guesses. Nobody can say they are wrong because there are a lot of resources in the ground."

As well as the price problem, he suspects that the number of so-called "sweet spots" – places where oil can be extracted at commercial rates – is less than previously thought. "This is why I believe that shale gas production in the US will peak in 2015, and will peak for oil just a few years later," he says.

While the world waits to see whether this sobering prediction turns out to be correct, unconventional hydrocarbons in Britain face tougher challenges. Above all, most experts agree that they will be more expensive to extract than Stateside, touting rates for shale gas around the $8 per million cubic feet mark.

Professor David Elmes, an energy specialist at Warwick University, says: "The US has an existing network of pipelines ready to transport the gas. There has always been a significant onshore drilling industry and tens of thousands of companies who can do the work. Environmental regulations in the US have been progressing, but let's say they have been keeping pace with the industry rather than constraining it.

"And a lot of developments have been made easier by the fact that the people who have hydrocarbons under their land own the hydrocarbons and can get paid significant amounts of money to let the developments occur."

It is hard to imagine the community benefits schemes being put forward by the Coalition competing with the sorts of windfalls that have been experienced by farmers in the US Midwest. It also raises the prospect that mark-up on shale oil in the UK might put the product beyond what is affordable.

COMPANIES working in this field in Scotland include Dart Energy and Reach CSG. Dart, an Australian company which wants to start commercially extracting methane gas out of a site near Airth in the Forth Valley, had been expecting to start the job last year.

It signed a five-year supply deal in 2011 with Scotia Gas Networks, which is part-owned by electricity giant SSE, that was estimated at the time to have been worth up to £300 million.

Dart had a few months earlier taken control of Composite Energy, the Scottish speculator that had been working on the acreage since the early 2000s.

It is not involved in fracking and is at pains to point out that it has no plans to become so. Indeed, as the Sunday Herald reports today (see page 19), it plans to give up the fracking licences it holds. Nevertheless, Dart's application to Falkirk and Stirling councils received 700 objections from local people and the two authorities declined to reach a decision, leaving the company with little choice but to turn to the Scottish Government.

The decision now sitting in the Government's in-tray is the first time that any UK authority has had to rule on whether to approve such a project.

The other major operator in the Scottish industry, Reach CSG, is planning to drill its first test borehole at Deerdykes, near Cumbernauld, in the autumn, tapping into the same West Lothian oil shale as Dart, and also focusing on coal bed methane.

In the eyes of managing director Graham Dean, these efforts are about returning the industry back to its Lowland roots (though there looks to be potential in Caithness and Orkney too). James Young set up the first commercial plant in Bathgate in the 1850s to convert coal into oil before shifting to a plant at West Calder that operated for nearly 100 years.

Dean points out that people extracted gas through fracking near Bargeddie church on the eastern outskirts of Glasgow in 1990, though they were not able to make it commercially viable.

To get over the same hurdle, he says that Reach needs a gas price equivalent to about $7.50 per million cubic feet. He is not particularly worried about the US price crash repeating here. "It would stop the North Sea first. It costs about 10% to 20% more to produce natural gas in the North Sea than it will here," he says.

Other industry voices agree that investors are quite relaxed about this situation. Elmes is not so sure. "Are other countries concerned about a boom bust in gas prices in the States? Yes," he says. "Are they now wondering how to get it started and not end up with a bust that stops shortly afterwards? Yes. That's the challenge for companies and governments."

Regardless of who is correct, the industry would certainly not deny that it has a public relations problem. The public in Scotland have been raising hell over everything from the Beauly-Denny electricity line to the creation of wind farms, so it is not surprising that fossil-fuel extraction on their doorstep is not exactly going down well.

Alongside its Deerdykes activity, Reach has had a planning application for test drilling refused at Moodiesburn, and is hoping for better luck with another application in Shotts. Dart is gearing up to ask permission to drill at another site in Dumfries and Galloway, while the UK Government is planning to allocate new exploration licences in the central belt next year. Dean believes that the Scottish Government needs to come out in support of the industry if it is to succeed – a prospect that would no doubt horrify environmentalists.

"The Westminster government is openly and unambiguously supportive. The Scottish Government needs to be the same, otherwise jobs will leak away from Aberdeen to the north of England. There needs to be a shale gas industry in Scotland as well," he says.

"The West Lothian oil shale has got enormous potential for shale gas. It could be very significant. As a rough guess, there's probably about 20% of what the BGS has announced for the north of England. It has the potential to create between 5000 and 10,000 jobs. It's more than enough to keep Scotland happy for a long time."

Whether that will ever be enough to win the argument, you suspect it has some way to run yet.