Natural gas production in the Rockies, like the country overall, is at vigorous levels this fall even as demand from western markets eases. The result: stout supplies in storage and soft prices.

Mountain region inventories were 23.5% higher than the five-year average as of Nov. 24, the most recent storage update from the Energy Information Administration (EIA) shows. While stocks are up everywhere on robust output and modest weather-driven demand, the Mountain region surplus far exceeds the national surfeit – 8.6% – and every other section of the country. At 10%, the Pacific region is the only other to post a double-digit surplus to the five-year average, EIA said.

Aside from last winter, California demand for Rockies gas “has been...