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We analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature (T) and pore water pressure (P_p) on the sliding behavior of faults. Rate‐stepping sliding tests were performed on laboratory faults in granite containing “gouge” (granite powder), both dry at 23° to 845°C [Lockner et al., 1986], and wet (P_p = 100 MPa) at 23° to 600°C [Blanpied et al., 1991, 1995]. Imposed slip velocities (V) ranged from 0.01 to 5.5 μm/s, and effective normal stresses were near 400 MPa. For dried granite at all temperatures, and wet granite below ∼300°C, the coefficient of friction (μ) shows low sensitivity to V, T, and P_p. For wet granite above ∼350°, μ drops rapidly with increasing T and shows a strong, positive rate dependence and protracted strength transients following steps in V, presumably reflecting the activity of a water‐aided deformation process. By inverting …