Degassing process

A process for the polymerization of olefin monomer(s) selected from the group consisting of (a) ethylene, (b) propylene, (c) mixtures of ethylene and propylene and (d) mixtures of (a), (b) or (c) with one or more alpha-olefins in a fluidized bed gas phase reactor, said process comprising passing a gaseous mixture of said olefin monomer(s) through the fluidized bed under effective polymerization conditions to provide a polymer product containing unreacted monomer(s) and a gaseous effluent stream containing unreacted monomer(s), removing the polymer product to a degassing vessel, splitting the gaseous effluent stream into first and second portions, recycling the first portion of the gaseous effluent stream to the fluidized bed, removing heavy hydrocarbons from the second portion of the effluent stream and returning said heavy hydrocarbons to the gaseous effluent stream for recycle to the fluidized bed, removing unreacted monomer(s) from the second portion of the effluent stream so that the amount of unreacted monomer(s) in the second portion of the effluent stream is <10% and returning said unreacted monomer(s) to the gaseous effluent stream for recycle to the fluidized bed, thereafter passing the second portion of the gaseous effluent stream to counter currently contact the polymer product in said degassing vessel to produce a polymer product having a reduced amount of unreacted monomer(s) and recycling the second portion of the effluent stream after passage through the degassing vessel to the gaseous effluent stream.