A baseline determination of CO2 and CH4 fluxes and soil-gas concentrations of CO2 and CH4 was made over the Teapot Dome oil field in the Naval Petroleum Reserve 3 in Natrona County, Wyoming, United States. This was done in anticipation of the experimentation with CO2 sequestration in the Pennsylvanian Tensleep Sandstone underlying the field at a depth of 5500 ft (1680 m). The measurements were made in January 2004 to capture the system with minimum biological activity in the soils, resulting in a minimum CO2 flux and a maximum CH4 flux. The CO2 fluxes were measured in the field with an infrared spectroscopic method. The CH4 fluxes were determined from gas-chromatographic measurements on discrete samples from under the flux chambers. The CO2 and CH4 were determined at 30-, 60-, and 100-cm (11, 23, and 39-in.) depths in soil gas by gas chromatography. A total of 40 locations had triplicate flux measurements using 1.00-m(2) (10.763-ft(2)) chambers, and soil gas was sampled at single points at each of the 40 locations. Carbon dioxide fluxes averaged 227.1 Mg CO2 m(-2) day(-1), a standard deviation of 186.9 mg m(-2) day(-1), and a range of - 281.7 to 732.9 mg m(-2) day(-1), not including one location with subsurface infrastructure contamination. Methane fluxes averaged 0.137 mg CH4 m(-2) day(-1), standard deviation of 0.326 mg m(-2) day(-1), and a range of -0.481 to 1.14 mg m(-2) day(-1), not including the same contaminated location.