A method of reducing reactor fouling in a polyketone polymerization process so as to allow continuous operation of the process. The method comprises contacting a mixture of carbon monoxide and one or more olefins in the presence of a suitable catalyst and a liquid diluent in a polymerization reactor characterized in that the gas head space in the reactor is no more than 5% of the total internal volume of the reactor or the polymerization reactor has substantially no head space. Where a loop reactor is employed, fouling of the loop conduit is reduced by maintaining the contents of the loop conduit in a turbulent state and above a minimum flow velocity.