Cyclic olefin metathesis polymerization catalyst comprising metal compounds wherein said metals consist essentially of a minor amount of a transition metal which Will initiate ring-opening metathesis polymerization of a cyclic olefin and a major amount of at least one second metal which will propagate the polymerization, wherein said catalyst is essentially devoid of pyrophoric metal compounds, e.g. metal alkyls, and preformed metal carbenes. A preferred transition metal is ruthenium. Said second metal can comprise aluminum, copper, hafnium, iron (III), iridium, manganese, molybdenum, nickel, niobium, rhenium, rhodium, tantalum, titanium, tungsten, yttrium, a Lanthanide, zinc or zirconium or a mixture thereof. Using such catalyst cyclic olefin, e.g. norbornene derivatives, can be polymerized, e.g. in an extruder, even in the presence of water.