Hydroformylation of 1-octene was studied in a two-phase system using [RhCl(1,5-COD)](2) complex catalyst and the trisodium salt of tri(m-sulfophenyl) phosphine (TPPTS) as a water soluble ligand. The reaction was carried out in a batch reactor at pressures between 1.5 to 2.5 X 10(3) kPa and temperatures of 333 and 343 K. Ethanol was added as a cosolvent to enhance the octene solubility in the aqueous phase and a buffer solution of sodium carbonate and bicarbonate was used to eliminate the formation of acetals. The hydroformylation products were n-nonanal and 2 methyl nonanal with a selectivity to linear aldehyde of about 80%. The reaction is first order with respect to octene and catalyst concentrations. The dependence on the carbon monoxide pressure was found to be complex with an enhancement at low partial pressures and an inhibition rate at high pressures. The reaction rate increased with the hydrogen partial pressure. A thermodynamic analysis concerning the solubilities of octene and gases in the reaction medium was studied and a semiempirical kinetic model was used to describe the rate of reaction.