We performed laboratory friction experiments on simulated fault gouges, measuring both the velocity- and slip-dependence of friction in velocity-step tests. Here, we evaluate the relative importance of slip- and velocity-dependent friction in laboratory velocity-stepping experiments, and assess the impact of friction slip dependence on natural faults.As an analogue fault gouge, we used a mixture of silt-sized quartz and commercially obtained clay-rich sediment (Grüne Tonerde, Argiletz Laboratories) mixed with deionized water. All tests were conducted at an (effective) normal stress of 2 MPa, with total shear displacements of up to ~16 mm.