Mr. Groppe says that while the average depletion rate in conventional gas wells is about 25 per cent (in other words, if you didn't drill at all for new wells, production would decline by a quarter each year), shale gas shows even more rapid depletion - output tumbles, on average, 45 per cent in the first year for shale wells.

Drilling of shale plays has recovered rapidly from the slowdown during the recession - indeed, the count of active horizontal drill rigs in the United States has ramped up to record levels - which, because of the high initial production volumes that are characteristic of shale wells, has flooded the market with supplies and fuelled expectations of continued rapid growth. But given Mr. Groppe's depletion numbers, the high drilling pace may also be serving to drain the resource in the major shale pools even faster than they would otherwise.

As for the shorter-term supply picture, Mr. Groppe notes that for all that horizontal drilling frenzy, shale gas accounts for just 6 per cent of U.S. natural gas production.

In the other 94 per cent - conventional gas - the rig count is 70 per cent below the pre-financial-crisis levels of September, 2008, as low prices and high inventory levels have convinced producers to keep drills idled.

"With that extraordinary drop in drilling, the [production] decline rate from all these [non-shale] sources is accelerating - and will be much more than offset whatever increases you get in shale."

Eoin Treacy's view Unconventional gas, predominantly shale gas but also tight gas, is providing the bulk of new North American supply in a trend which shows no sign of slowing. Current prices are still well above the historic norm but relative to oil and coal are comparatively cheap. Unconventional gas shows every sign of being a game changer for the natural gas market and prices suggest its impact has not yet been fully digested by investors. At a certain price level, it will simply be uneconomic to continue to drill new wells. When that is reached, any supply glut will quickly be expended and prices will rise back to at least economic levels.

At today's $3.90, one can reasonably ask how economic it is to keep drilling new wells. However, while prices have lost momentum somewhat, a sustained move above $4.25 is needed to indicate demand has regained the upper hand.