Abstract A review of gas relative permeability ( k rg ) studies of low-permeability sandstones indicates that they can be modeled using the Corey equation, but scarce data near the critical gas saturation ( S gc ) limit k rg modeling at high water saturations. Confined mercury injection capillary pressure and coupled electrical resistance measurements on Mesaverde sandstones of varied lithology were used to measure critical nonwetting saturation. Most of these data support the commonly applied assumption that S gc < 0.05. However, a few heterolithic samples exhibiting higher S gc indicate the dependence of Sgc on pore-network architecture. Concepts from percolation theory and upscaling indicate that S gc varies among four pore-network architecture models: (1) percolation ( N p ), (2) parallel ( N // ), (3) series ( N ┴ ), and (4) discontinuous series ( N ┴d ). Analysis suggests that S gc is scale- and bedding-architecture-dependent in cores and in the field. The models suggest that S gc is likely to be very low in cores with laminae and laminated reservoirs and low (e.g., S gc < 0.03–0.07 at core scale and S gc < 0.02 at reservoir scale) in massive-bedded sandstones of any permeability. In cross-bedded lithologies exhibiting series network properties, S gc approaches a constant reflecting the capillarypressure property differences and relative pore volumes among the beds in series. For these networks, S gc can range widely but can reach high values (e.g., S gc < 0.6). Discontinuous series networks, representing lithologies exhibiting series network properties but for which the restrictive beds are not sample spanning, exhibit S gc intermediate between N p and N ┴ networks. Consideration of the four network architectures lends insight into the complications of heterogeneous lithologies at differing spatial scales and underscores the difficulty of upscaling laboratory-derived relative permeabilities for reservoir simulation. Analysis also indicates that for some architectures, capillary pressure and relative permeability anisotropy may need to be considered.