We apply a hybrid data-driven and physics-based method to predict the most likely futures of gas production from the largest mudrock formation in North America, the Marcellus Shale play. We first divide the ≥100,000 mi2 of the Marcellus Shale into four regions with different reservoir qualities: the northeastern and southwestern cores and the noncore and outer areas. Second, we define four temporal well cohorts per region, with the well completion dates that reflect modern completion methods. Third, for each cohort, we use generalized extreme value statistics to obtain historical well prototypes of average gas production. Fourth, cumulative production from each well prototype is matched with a physics-based scaling model and extrapolated for two more decades. The resulting well prototypes are exceptionally robust. If we replace production rates from all of the wells in a given cohort with their corresponding well prototype, time shift the prototype well according to the date of first production from each well, and sum up the production, then this summation matches rather remarkably the historical gas field rate. The summation of production from the existing wells yields a base or do-nothing forecast. Fifth, we schedule the likely future drilling programs to forecast infill scenarios. The Marcellus Shale is predicted to produce 85 trillion SCF (TSCF) of gas from 12,406 existing wells. By drilling ∼3700 and ∼7800 new wells in the core and noncore areas, the estimated ultimate recovery is poised to increase to ∼180 TSCF. In contrast to data from the Energy Information Administration, we show that drilling in the Marcellus outer area is uneconomic.