The wide range of bearing types and operating conditions precludes any simple, all-inclusive statement or guideline allowing the selection of the proper lubricant. At the design level, the first consideration is whether oil or grease is best for the particular operation. When heat must be carried away from the bearing, oil must be used. It is almost always preferred for very high-speed applications. Grease lubrication is generally applicable to low-to-moderate speed applications that have operating temperatures within the limits of the grease.