Process for producing polyethylenes having a broad molecular weight distribution, and a catalyst system used thereby

A process for the polymerization of ethylene and optionally alpha-olefins to form ethylene homopolymer or copolymers having a broad molecular weight distribution, comprising polymerization of 100-80 wt. % of ethylene and 0-20 wt. % of comonomer in the presence of two independent, simultaneously present catalysts A and B, wherein catalyst A, deposited on an inorganic support, comprises chromium in a predominantly oxidant state of 2 and catalyst B comprises a bis-cyclopentadienyl chromium compound reacted with an inorganic support.