Abstract
Estimates have been made by ten different groups of different categories contributing to potential gas resources for the USA. The estimates are evaluated using probabilistic methods to determine both the most likely values of potential reserves (or resources) in a given category, and also to assess the range of uncertainty of each category, i.e. the volatility of each estimate.
In the case of conventional existing gas fields, where the most copious and most accurate data are available from which an estimate can be constructed, the range of uncertainty is about 40%. In the cases of all other more speculative resource categories the range of uncertainty is at least 75% and as high as 160% for shale gas.
Estimates of the total Lower 40 States reserves are uncertain by about 80% and for the total 50 United States by 70%. A total reserve estimate, risk-weighted inversely with the volatility of each category, would suggest a likely discoverable gas reserve of greater than 110 Tcf (90% chance), less than 260 Tcf (90% change, and probably (2/3 chance) less than about 190 Tcf. It is also 5 times as likely that the majority of this discoverable gas will be in existing and discoverable fields in the Lower 48 States together with tight sands, as compared to anywhere else in the nation or in any other category.
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