Creep behaviour of two types of superalloy single crystals of the orientation < 001 > was studied at 850 degrees C in air to assess their relative suitability for turbine blade applications: CMSX-4 and its potential low cost alternative, CM186LC. The chemical composition of these two superalloys is similar, their microstructure, especially gamma/gamma' distribution, differs substantially. At the same applied, stress, the time to failure of CM186LC is shorter than that of CMSX-4. Simultaneously, the creep rate of CM186LC is higher than that of CMSX-4 for the whole lifetime. This is attributed to easier activation of dislocation sources within large gamma'particles present in CM186LC crystals.