High-pressure mercury capillary pressure curves have been measured on 92 plugs obtained from the core from two Barnett-shale gas wells. The curve set consists of four basic types: Type 1, incremental intrusion curve with maximum; Type 2, incremental intrusion curve "flat" at 60,000 psi; Type 3, no apparent maximum; and Type 4, no mercury intrusion. For all types, the mercury porosity is less than the helium porosity. This is most likely because of surface forces, not the size of the mercury atom. The curve types cluster by depth and correlate to other rock properties. Permeability estimated from the mercury capillary pressure curves is in the 1-to 10-nanodarcy range.