A continuous process and system for producing polyether polyols that allows for continuously adding an unreacted oxide to a loop reactor while adding at least one thermally deactivating catalyst capable of thermally deactivating prior to decomposition of polyether polyol which can allow for greater concentrations of unreacted oxides and/or a rate of reaction in the loop reactor is at a rate at least two times faster than a rate of reaction in a loop reactor containing less than 14 weight percent unreacted oxide. In a preferred embodiment, the catalyst is a double metal cyanide catalyst and a plug flow reactor is formed in series with the loop reactor wherein neither reactor contains a vapor space.