In terms of reducing power losses and ensuring optimal lubrication, a high viscosity index is crucial for lubricants exposed to changing load or temperature conditions. Several studies suggest that an enormous improvement of the viscosity-temperature characteristics could be achieved by the application of dissolved CO2 on various base oils. The direct link between the applied pressure and the lubricant viscosity offers the possibility of adjustable and thus tunable lubricants. The practical implementation of dissolved CO2 as a viscosity index improver is investigated on a roller bearing test rig. The results indicate a significant reduction of power losses and show that it is possible to influence the friction condition in the rolling contact through viscosity adaptation.