From seskate.com Lubricant - What is it? The two most common lubricants are grease and oil. Grease is basically oil with a thickener or soap. The thickener acts like a sponge to soak up the oil when not in use. What does it do? * keeps metal parts from wearing against one another * keeps dirt away from the sensitive inner workings Grease*****************************Oil helps keep dirt out****************prevents material wear can suspend contaminants******requires frequent servicing prevents material wear***********has low torque requires little servicing**********does not last as long increases torque lasts a long time From the above you can see that a greased bearing requires little servicing yet cannot run as fast as an oiled bearing. An oiled bearing is susceptible to dust and contamination so it needs to be serviced more often. As grease is thicker, it acts as a seal against dirt, but at the same time it can increase torque and slow down the bearing. belu