The influence of the hydration and the surface characteristics of five supports in the hydroformylation of oct-l-ene by supported aqueous phase catalysis (SAPC) using [Rh-2(mu -(SBu)-Bu-t)(2)(CO)(2) (TPPTS)(2)] as catalyst was studied. The results confirm that the size of the pores and the amounts of water were found to be the determining factors contributing to the SAPC. According to the size of pores there is a critical value for which the SAPC takes place either in the classical model or in conditions where the pores are filled. When the pores are fully filled the SAPC can operate efficiently onto the external surface, stabilising the conversion in a relatively wide range of support hydration.