For a quarter of a century, an unassuming pipeline junction in Erath, Louisiana, known as the Henry Hub has been the lodestar for US natural gas traders, sending out pricing cues for a vast array of financial products.

But over the past half-decade, the new technologies of hydraulic fracturing and horizontal drilling have redrawn the map of North American gas production. In particular, output has surged in the Marcellus Shale, the gas-rich geological formation spreading across New York, Ohio