Nuclear and massive hydraulic fracturing (MHF) projects in the Pieance Creek basin, Colorado, are aimed at recovering appreciable fractions of the large volumes of gas in place in low-permeability, discontinuous sandstone units of the Mesaverde and Fort Union Formations. Most of the gas-bearing rock consists of lenticular channel-fill sandstones. Although an average individual lens exhibits 2 interconnections or interpenetrations along its length, only a fraction of the gas in place in a 640-ac area is even tenuously interconnected. Successful massive fracturing projects will connect larger amounts of the gas in place to the well bore, and will greatly increase the rate of production. Project Rio Blanco, a nuclear gas stimulation experiment, and the Rio Blanco MHF experiment, are in the evaluation and fielding stages, respectively. Project Rio Blanco involved the simultaneous detonation in May 1973 of three 30-kt nuclear explosives placed about 400 ft apart vertically in a single well bore. Current information indicated an unpredicted lack of communication among breccia chimneys produced by the detonation. Plans are underway to use a different reentry technique to obtain data from the lower chimneys. Until these data are available, no judgment can be made as to the success or failure of the experiment. The Rio Blanco MHF experiment is being fielded about 1 mi north of the Project Rio Blanco nuclear well. The MHF experiment is an attempt to stimulate a 1,300-ft section of Fort Union and Mesaverde gas-bearing sandstones equivalent to the section fractured in the Rio Blanco nuclear well. Results from Rio Blanco MHF experiment will not be available for about 18 months. At that time, a comparison will be made between the efficiencies of nuclear and massive hydraulic fracturing.