Abstract: This invention comprises the novel composition formed by mixing (A) a chromium tris-diorgano-orthophosphate of the general formula Cr[OP(O) (OR).sub.2 ].sub.3 wherein R can be an alkyl, alkoxyalkyl or cycloalkyl group of one to about eight carbon atoms and the chlorinated and brominated derivatives thereof, (B) an alkyl aluminum compound of the general formula R'.sub.2 R"Al in which each R' and R" can be an alkyl group of 1 to 6 carbon atoms and each R" can also be a hydrogen atom, and (C) a halogenated olefin of four to about eight carbon atoms containing at least four halogen atoms at least two of which are attached to doubly bonded carbon atoms.This invention also comprises the use of this novel combination as a catalyst for the polymerization of ethylene alone or with propylene and other olefins. This invention also comprises the polymer products prepared by said method.