A plan has been developed to produce the Wasson San Andres Denver Unit (DU) gas-cap reserves without adversely affecting the existing tertiary CO2 flood of the oil column. Reservoir-characterization studies validated hydraulic isolation between the uppermost San Andres gas-bearing zones and the oil-bearing zones currently under water and CO2 flooding. Field testing programs proved the technical viability of producing the gas cap without affecting the oil column. A Wasson field, 3D, fully compositional simulation model was used to predict effects on the oil column and develop gas-production forecasts.