An automated constant pressure reactor for measuring the solubilities of slightly soluble gases in aqueous solution is described. The apparatus can also be used for kinetic studies of aqueous reactions involving a gaseous reactant or product. Thc system can be operated unattended and therefore can be used for prolonged experimentation. Results obtained using the apparatus for solubilities of methane and butane in triple distilled water at atmospheric pressure and 2SoC are compared with those reported in the literature.