The volcanic Ascension Island is located about 100 km west of the median valley of the Mid-Atlantic Ridge. A 3126 m-deep well was drilled on the island to investigate the geothermal system associated with the recent volcanism. Two types of fluid were encountered in the well, both derived from seawater. The first fluid, found at 2500 m depth, was a recent mixture of a gaseous phase rich in volcanic CO2 and a geothermal fluid. Flow from this entry was so rich in gas that a CO2-H2O froth was formed in the wellbore. The second fluid was water produced by a gas lift from near the bottom of the well at 2957 m. The water appeared to have normal gas concentrations. The geothermometer temperatures of water from the shallow and deep fluid entries were 200 and 245 degrees C, respectively. The geothermometer and the measured temperatures were in close agreement, suggesting low permeability in the geothermal system.