The steady-state compressive creep of Al2O3 with 10 vol% SiC whiskers having grain sizes of 1.2, 2.3, and 4.0 mum has been measured at 1400 degreesC in argon. The creep rate is related to the free volume within the whisker network, not the nominal grain size. The results are consistent with diffusional-controlled creep with different contributions from grain-boundary sliding. Under low stresses, only Liftshitz sliding is possible and the diffusional process controls deformation, while at stresses over a threshold, Rachinger sliding is the mechanism controlling deformation. The evolution between Liftshitz and Rachinger sliding is marked by a significant increase in the value of the stress exponent.