The creep behavior and microstructure of several nickel-base single-crystal superalloys after high-temperature low-stress creep have been investigated. These alloys were designed with varying content of the alloying elements Mo and Ru. At 1100 degrees C and 137 MPa, the large gamma/gamma' lattice misfit in negative with the addition of Mo leads to the formation of dense interfacial dislocation networks. These dislocation networks are effective to strengthen the alloys during creep by preventing the penetration of the gamma dislocations into the gamma' phase.