Middle to Upper Devonian Horn River strata in British Columbia, western Canada, has become a proven province of commercial shale gas resource in the last few years. The shale gas resource potential in the Horn River Basin has been historically assessed based on reservoir volumetric characteristics. However, as fundamental mechanisms controlling shale gas ultimate recovery remain poorly understood, the classic theories and simulation techniques applied to evaluate recoverable gas for conventional reservoir have proven inadequate for shale gas reservoirs. Determining the ultimate recovery from production data at the well level and projecting these data to the basin level to establish the ultimate recoverable resource may provide a more realistic estimation for long-term sustainable development planning. This paper analyzes well performance of 206 wells using Arps and Valko models in the Horn River Basin with adequately protracted production records and projects these performances to the future to assess the ultimate recovery of shale gas resource. This process yields a mean estimate of recoverable methane gas resource of 114 TCF (1 TCF (trillion cubic feet) = 28.3 × 109 m3), with a large uncertainty range of 38–217 TCF (90%–10% confidence interval). This study also suggests that the drastic variation in estimated ultimate recovery (EUR) from wells across the basin is attributed primarily to the intrinsic geological character of the shale reservoir, though advances in technology and industry practice may also contribute in some degree to this variation.