For heavily soiled greasy ovens it is best to use Steam, with the nylon brush' and a cloth/paper towel. Start inside the oven from the ceiling steaming in small areas to melt the grease and then wipe away with the cloth. Repeat this process from top to bottom until the oven is cleaned. The same tool and process can also be used on the oven door. For very stubborn baked on grime try a stiffer brass brush or steel wool can be used providing it does not scratch the surface.