Abstract: Alkylene carbonates, particularly ethylene carbonate, are prepared by the reaction of an alkylene oxide with carbon dioxide in the presence of a catalyst at temperatures ranging upwards from 20.degree. C., particularly temperatures above about 90.degree. C., preferably 90.degree.-170.degree. C. The conversion of alkylene oxide to alkylene carbonate can be carried out in the presence of water while minimizing the undesirable hydrolysis of the carbonate to the corresponding alkylene glycol and formation of higher glycols. This is achieved by maintaining the water to alkylene oxide molar ratio and the carbon dioxide to alkylene oxide ratio within the stated limits and adjusting the carbon dioxide partial pressure to provide the desired selectivity to alkylene carbonate.