Method of polymerizing olefins

The method of making polymers from polymerizable 1-olefins which comprises polymerizing at least one of said olefins under polymerizing conditions with a catalyst system consisting essentially of the reaction product prepared by reacting together at an elevated temperature (1) a support which is a finely divided insoluble inorganic support material of the class consisting of silica, alumina, zirconia and mixtures thereof modified by reacting said support with a compound of the class consisting of alkyl esters containing 1 to about 7 carbon atoms in the alkyl group and halides of titanium, zirconium, nickel and mixtures thereof in amounts to give about 0.5-10% metal on the support (2) an organotin chromate essentially of the formula ##EQU4## and (3) a cocatalytic amount of an alkyl aluminum compound of the formula R.sub.a AlX.sub.b in each of which formula each R is an individually selected hydrocarbon radical containing from 1 to about 14 carbon atoms, X is a member of the class consisting of halogen, hydrogen and alkoxy, a is an integer from 1 to 3 inclusive and b is an integer from 0 to 2 inclusive, with the sum of a and b being 3, the said system having an aluminum-chromium ratio of at least 2 to 1.