Tensile creep tests in the [011] direction have been performed on two specimens of SRR99 at 1173 K under a load of 300 MPa. The microstructure was analysed by transmission electron microscopy investigations after plastic strains of 0.1% and 0.29%. At both strains, the γ′ phase is not sheared by dislocations. Plastic deformation is concentrated in roof matrix channels lying at an angle of 45° to the load axis. Gable matrix channels that contain the load axis are almost free of dislocations. This experimental result was shown to be due to the superposition of coherency and external load stress tensors, leading to different levels of shear stress in the two types of matrix channel. The results obtained at 1173 K are compared with previous results at 1033 K.