The invention relates to a process for the hydroformylation of olefins with synthesis gas by using an SILP catalyst comprising at least one spherical catalyst particle of radius R, and is characterized in that the ratio of the concentration of a component i to the concentration thereof at the surface of the SILP catalyst particle is defined as a function of a position x by the following relation: (shown in the description), where SILP is a dimensionless number in respect of the spherical catalyst particle relating the mass transfer, in the pore, across the phase interface between gas and ionic liquid and in the ionic liquid to the reaction.