Argon gas was trapped at high pressure within hollow carbon tubes grown in vapor that have an outer diameter of between 20 and 150 nanometers. The gas was forced into the tubes by hot isostatically pressing (HIPing) the carbon material for 48 hours at 650 degrees C under an argon pressure of 170 megapascals. Energy dispersive x-ray spectroscopy maps and line scans across the tubes show that the argon is trapped inside the bore and not in the tube walls. The room temperature argon pressure in these tubes was estimated to be about 60 megapascals, which indicates that equilibrium pressure was attained within the tubes at the HIPing temperature. These findings demonstrate the potential for storing gases in such carbon structures.