PURPOSE: To provide the subject process wherein the produced polymer has a high average molecular weight, and the polymerization rate is considerably high at the same reaction temperature as compared with that in polymerization in a non-polymerizable liquid diluent.

CONSTITUTION: A linear alternating polymer of carbon monoxide with one or more olefins having 3-10 carbo atoms per molecule and optionally an ethene is produced by contacting the monomers at elevated temperature and pressure in the presence of a liquid diluent substantially consisting of the 3-10C olefins as monomers with a suitable catalyst comprising palladium as a metal of group VIII and, in addition to the metal of group VIII, a bidentate ligand which can form a complex with the metal of group VIII through two phosphorus and nitrogen and/or a sulfur-containing dentate group, the catalyst comprising an anion of an acid with a pKa of below 4.