Alkylene oxide adducts of organic compounds having active hydrogen atoms are prepared by a process which comprises contacting and reacting an alkylene oxide reactant comprising one or more vicinal alkylene oxides with an active hydrogen containing reactant comprising one or more compounds having active hydrogen atoms in the presence of a catalytically effective amount of one or more compounds of one or more of the rare earth elements. The product alkoxylates are known to be useful, for instance, as nonionic surfactants, wetting and emulsifying agents, solvents, and chemical intermediates.