Estimates of gas in place (GIP) for the Marcellus Shale can be calculated from analysis of the organic-rich rock by programmed pyrolysis. The GIP is a function of several factors, including the original hydrocarbon-generation potential of immature shale (S_2o) as measured by programmed pyrolysis; a conversion factor (C) to determine the gas-volume equivalent generated by cracking of kerogen, bitumen, and oil; the thickness (t) of organic-rich shale; organic richness (O) compared with a standard sample; the transformation ratio (TR) of kerogen to hydrocarbon; and percent retention (R) of gas after primary migration. In particular,

Technically recoverable reserves are computed to be 20% of the GIP. By way of example, our calculated GIP for Steuben County, New York, is 39 bcfg/mi², and that for Broome County, New York, is 217 bcfg/mi², a fivefold increase within 100 mi (161 km). Because geologic controls over GIP vary so greatly across the Appalachian Basin, gas resources and reserves should properly be calculated from local geochemical data.