For gears that are operated at slow speeds, wear is often the failure mode that limits gear lifetime. Gears running at slow speeds are often lubricated with grease. The composition of the grease has a significant effect not only on gear lifetime but also on lubrication costs. Therefore, the selection of a suitable grease for a given gear application requires a good knowledge of its expected performance in regard to wear. In order to better understand the wear behavior of gears lubricated with grease, an understanding of the influence that different grease components, e.g., base oil type and viscosity, thickener type, additive type, and solid lubricants, have on gear wear behavior is important. In this paper, systematic investigations on the influence of different grease components on the wear behavior of slow running, case carburized gears were conducted using the FZG back-to-back gear test rig. The emphasis of the experimental work presented herein lies on the effect that the base oil viscosity and type, additive type, type of soap thickener, as well as the type and concentration of solid lubricants have on the gear wear behavior at low pitch line velocities. The investigations showed that the base oil type and viscosity only have a slight effect on gear wear behavior under boundary lubrication conditions. However, the thickener type and especially the additive type as well as the solid lubricant type significantly affect the wear behavior of gears running at slow speeds and lubricated with grease.