A process for the production of an ester comprises reacting an olefin with carbon monoxide, hydrogen and another ester at elevated temperature and pressure in the presence of a catalyst comprising (1) a rhodium source, (2) a ruthenium source, and (3) cobalt or zinc iodide. The product ester comprises the acid group of the ester used as reactant esterified with a hydrocarbyl group derived from the olefin, hydrogen and carbon monoxide.