This paper reports experimental values of the surface tension between CO2 gas and tetra-n-butylammonium bromide (TBAB) aqueous solution measured by the pendant drop method. The experimental conditions were pressures from 1.00 MPa to 4.00 MPa, temperatures from 288.15 K to 303.15 K and w(TBAB) from 0.10 to 0.40, where w(TBAB) denotes the mass fraction of TBAB in the aqueous solution. These pressure-temperature-composition conditions partially fall into the stability zone of (CO2 + TBAB) semiclathrate hydrate but all data were obtained without any hydrate in the system. Surface tension decreased with increasing w(TBAB) and pressure but temperature dependency was not observed. Compared to the air-TBAB aqueous solution system and CO2-water system, the values of the surface tension were smaller. (C) 2015 Elsevier Ltd. All rights reserved.