LONDON, Aug. 27 -- Europe's gas storage problem has a name now, and it is not one a continental energy ministry wants to hear in late August. At 63 percent of capacity, the EU's underground reserves are the thinnest they have been at this point in any year since 2009 - the last time a supply rupture forced the bloc to improvise through winter. The shortfall is not a statistical footnote. It is the number behind every price move in the natural gas market this week, and it explains why a modest uptick in American heat demand has translated into something more consequential for European industry.

Henry Hub, the US benchmark, settled at $2.90 per million British thermal units on Wednesday, a gain of roughly one percent and the highest close ...