The wear behavior of grease lubricated gears is significantly affected by a number of factors besides the composition of the grease that is used for lubrication. A main influence factor on the wear behavior of grease lubricated gears is the lubrication supply mechanism (“circulating” or “channeling”), which is, among other things, strongly affected by the rotational speed of the gears. Especially at higher rotational speed, the dominant grease lubrication supply mechanism for grease lubricated gears tends to be “channeling”, which generally promotes increased wear on account of limited lubricant availability in the mesh as well as limited heat dissipation from the mesh. Experimental investigations conducted herein have shown that the gear wear behavior, especially at higher rotational speed, can be influenced by the internal geometry of the gear casing as well as by the direction of rotation of the gears. Additional investigations that were conducted focus on the effect of the material pairing and heat treatment on the wear behavior of grease lubricated gears in comparison to a case-carburized reference gear set. Furthermore, the effect of the gear size on the lubrication supply mechanism and thus on the wear behavior was investigated. For both gear sizes investigated (mn = 1.0 mm and mn = 0.6 mm), circulating was observed at low rotational speeds. At high rotational speeds, channeling effects were dominant.