It is important to clarify the parameters which influence the creep rupture life of Ni-base single crystal superalloys under the service condition of jet-engine turbine blades, such as 1000°C/245 MPa. In the most recently developed alloys, Ru is added to suppress the formation of the detrimental Topologically Close Packed (TCP) phases, however, its solid solution strengthening effects have not been clarified yet. In this study, the parameters affecting the creep rupture life of alloys with various compositions were analyzed by a multi regression method, and the results were discussed quantitatively in terms of the chemical composition of the γ′ phase, lattice misfit and volume fraction. It was found that Re, Mo, Ta and W were all effective additions for solid solution strengthening and Re was found to be the most effective under the service condition. In contrast, Ru addition had almost no influence on the strengthening effect. The results enabled the prediction of the creep rupture life of an alloy of a known composition.