Olefins are converted to aldehydes and/or alcohols having one more carbon atom than the olefin by reacting the olefin with carbon monoxide and hydrogen in the presence of an in situ formed catalytic complex of a Group VIII metal, carbon monoxide and a trivalent ligand, the metal being introduced into the reaction zone in the form of a solution of a water-soluble inorganic salt dissolved in a solvent comprised of at least 40% by volume of a polyalkylene glycol, the polyalkylene glycol acting as a coupling agent preventing precipitation of the metal prior to formation of the catalyst complex.