A gas-phase olefin polymerization process in a plug flow reactor uses a catalyst
system containing a magnesium halide supported titanium-containing component, an
organoaluminum component, and at least one external electron donor component; in
the process a first external donor component is added to the reactor at an injection
point axially near an injection point for the supported transition metal containing
component, and at least a second external donor component is added to the reactor
axially downstream from the injection point for the first external donor component.
