Abstract: The present invention relates to a gas fluidized bed process for the production of copolymers having a density between 0.900 and 0.935, which process comprises copolymerization of (a) ethylene, (b) propylene and/or 1-butene, and (c) alpha-olefins comprising from 5 to 8 carbon atoms in the gaseous state, in admixture with an inert gas and optionally with hydrogen, in the presence of a catalytic system comprising a cocatalyst consisting of at least 1 organo-metallic compound of a metal of groups II and III of the Periodic Table of Elements and a special solid catalyst.