The solubility of CO2 in pure water was investigated under high-pressure conditions, from 7 to 12 MPa. Temperature varied between 2.5-20 degrees C. CO2 clathrate hydrate formed at temperatures below approximately 10 degrees C. Saturated concentrations of CO2 were determined from expanding dissolved gas. The solubility in the presence of the hydrate decreased with decreasing temperature and with decreasing pressure, although some researchers reported it decreased with higher-pressure conditions at about 7 degrees C. Many other researchers reported that the pressure conditions did not affect the solubility in the presence of the hydrate. Although this is mostly correct, we did confirm a small difference in solubility due to pressure conditions. (c) 2005 Elsevier Ltd. All rights reserved.