A continuous process for carbonylation of ethylene in a liquid phase using carbon monoxide, a co-reactant and a suitable catalyst system, including: (i) forming a liquid phase comprising the co-reactant and a suitable catalyst system obtainable by combining: (a) a group VIII metal/compound; (b) a ligand of general formula (I) and c) optionally, a source of anions; wherein Q1 is optionally phosphorous; (ii) forming a gaseous phase in contact with the liquid phase by providing at least an ethylene gas input feed stream and a carbon monoxide gas input feed stream wherein the ethylene:CO molar ratio entering the liquid phase from the input feed streams is greater than 2:1; (iii) reacting ethylene with carbon monoxide in the presence of the co-reactant, and of the suitable catalyst system in the liquid phase; wherein the ethylene:CO gas molar ratio in the gaseous phase is between 20:1 and 1000:1 or wherein the molar ratio of ethylene:CO in the liquid phase is greater than 10:1.