Tunable solvent systems provide optimal reaction conditions for homogeneous catalysis as well as appropriate conditions for separating the product from the catalyst via temperature switches. Two tunable solvent systems are presented based on different thermodynamic concepts, namely thermomorphic multicomponent solvent systems and dispersions of immiscible liquids, stabilized by nonionic surfactants as microemulsions. Both systems were applied for the regioselective hydroformylation of the model substrate 1-dodecene with a Rhodium/ligand catalyst system. The accessibility of the catalyst for the reactants was compared between the molecularly dispersed mixtures and the colloidally dispersed microemulsion systems which are heterogeneous on the microscopic level.