Material-balance considerations can be successfully applied to high-rate Devonian shale oil and gas reservoirs to enable an estimation of reserves on an assumed abandonment pressure. The procedure uses Tracy's form of the Tarner material-balance method in conjunction with an empirically derived permeability-ratio curve. Necessary data are simply and economically collected early in the life of the well and include (1) production data for at least one continuous month, (2) corresponding initial and final measured bottomhole pressures (BHP's), (3) pressure-variant fluid properties, and (4) a representative permeability-ratio curve.