The Total Petroleum System approach was used to estimate undiscovered gas potential of the Wasatch Plateau and Castle Valley, central Utah. The Ferron Coal/Wasatch Plateau Total Petroleum System was geologically defined and subdivided into seven assessment units, six of which were formally evaluated. Geologic data considered in defining the assessment unit boundaries included thermal maturity, coal presence and thickness, overburden. thickness, and faulting intensity. Historical production data were also used to estimate volumes of gas from undrilled areas. The one conventional assessment unit includes almost the entire area of the petroleum system and is characterized by known accumulations that occur in structural or combination traps in sandstone reservoirs. The estimated undiscovered conventional producible gas that may be added to reserves of this unit ranges from a low (1795) of 14.8 billion cubic feet (BCFG) [419 million cubic meters (Mm(3))] of gas to a high (175) of 82 BCFG [2321 Mm(3)] and a mean value of 39.9 BCFG [1130 Mm(3)]. Continuous gas accumulations are those in which the entire assessment unit is considered to be gas-charged. Within these assessment units, there may be wells drilled that are not economic successes but all are expected to contain gas. Coalbed gas is in this continuous category. Mean estimates of undiscovered gas for the five continuous assessment units are: (1) Northern Coal Fairway/Drunkards Wash-752.3 BCFG [21,323 Mm(3)]; (2) Central Coal Fairway/Buzzard Bench-536.7 BCFG [15,194 Mm(3)]; (3) Southern Coal Fairway-152.6 BCFG [4320 Mm(3)]; (4) Deep (6000 feet plus) Coal and Sandstone-59.1 BCFG [1673 Mm(3)]; (5) Southern Coal Outcrop-10.6 BCFG [300 Mm(3)]; and Joes Valley and Musinia Grabens-not assessed. The mean estimate of undiscovered gas for the entire TPS is 1551.2 BCFG [43,914 Mm(3)]. There is a 95% chance that at least 855.7 BCFG [24,225 Mm(3)] and a 5% chance that at least 2504 BCFG [70,888 M(m)3] of undiscovered producible gas remain in the TPS.