Abstract: A process for the manufacture of olefin polymers in a continuous gas phase polymerization reaction wherein monomer, after passage through the fluidized bed, is cooled to a temperature below its dew point to produce a mixture of cold gas and liquid. All or nearly all of the cold gas is introduced into the bottom of the reactor to serve as the fluidizing gas stream for the fluidized bed. Cold liquid, separated from the mixture, is either injected directly into the peripheral region around the fluidized bed or onto the walls of the expanded section of the reactor to form a liquid film flowing down the wall of the reactor or alternatively, the cold liquid is warmed to form a heated fluid by passing in indirect heat exchange relation with the fluidized bed and is then injected directly into the peripheral region of the fluidized bed or onto the wall of the expanded section of the reactor to form a downward flowing stream of cold liquid.