The reentry drilling established communication with the top Rio Blanco detonation region at a depth of 1704 m, or ∼76 m above the top detonation center. A total of 2.8 × 106 m3 (98 × 106 ft3) of dry gas at standard conditions has now been produced during two separate test periods. Radioactive and chemical analysis of this gas and the modeling of the stimulated reservoir show the following main results: 1. No permeable connection exists between the top and the middle detonation regions, since no significant amount of the tracer incorporated in the center explosive canister was detected in the produced gas. As a consequence, results for the top detonation region only are available at this time. 2. The initial cavity radius is deduced to be 20 m (66 ft) or well within expectations. 3. Integration of the 85Kr produced indicates a yield of 34 ± 3 kt for the top explosive. 4. Of the ∼1000 Ci of tritium produced in the top explosion region, ∼5% is incorporated in the gas phase. 5. Pressure drawdown and buildup data are best reproduced by a two-layer reservoir model showing stimulated permeabilities ∼10 and 30 times original formation permeabilities, and extending to a distance of ∼3 cavity radii from the wellbore. 6. The capacity of the reservoir intercepted by the top explosive is deduced to be ∼0.2 millidarcy-meters (md-m) [0.73 millidarcy-feet (md-ft)], as contrasted with preshot estimates ranging from 1.3 md-m (4.1 md-ft) to 2.3 md-m (7.6 md-ft). Additional subsurface investigations of the other detonation regions, as well as a reevaluation of the initial reservoir properties, are in progress.