Homogenous catalysis is capable of a great variety of highly active and selective chemical transformations. However, separation and recycling of the catalyst is often the most economically important step of the process. A new biphasic approach has been proposed based upon ionic liquids (ILs) and compressed or supercritical CO₂ to aid catalysis and separation. Ionic liquids are organic salts liquid near ambient conditions. They have little measurable vapor pressure and have hence been touted as green solvents. Molecularly-designed salts are possible but they often become viscous liquids or even solids. Coupling ionic liquids with compressed CO₂ has numerous advantages, as most ILs are immeasurably insoluble in CO₂ and CO₂ is very soluble in the IL phase. CO₂ can also reduce the melting point of the salts and anecdotally has been ascribed to reduce viscosity and increase the diffusivity. However, there are no quantitative studies on the viscosity and diffusivity in these systems. This presentation will illustrate quantitatively for the first time, the effect of CO₂ concentration on the viscosity of ionic liquids. Models will be presented for in their ability for viscosity correlation and the CO₂ effect on the diffusivity will be discussed. These results will be shown as to their effect on Rhodium-catalyzed hydrogenation and hydroformylation of olefins in the biphasic IL/CO₂ system.