The Energy Information Administration (EIA) has a brief report on forward market prices for Appalachian Basin production: "Growth in natural gas production from the Marcellus region of Pennsylvania, West Virginia, and Ohio has lowered the spot price of natural gas at the TCO Appalachia trading point in recent years. Forward market prices for natural gas indicate that this production growth will continue, driving the price in this region below the benchmark Henry Hub price early next year."
A good introduction to the topic.