Lubricating oil used for bearing is usually a highly refined petroleum or synthetic oil which has a high film strength and superior oxidation and corrosion resistance. Petroleum oils have physical and chemical properties that can help in the selection of the correct oil for any bearing application. Synthetic oils cover a broad range of categories, and include polyalphaolefins, silicones, polyglycols, and various esters. In general, synthetic oils are less prone to oxidation and can operate at extreme hot or cold temperatures.

Physical properties such as pressure-viscosity coefficients tend to vary between oil types and caution should be used when making oil selections. The polyalphaolefins (PAO) have hydrocarbon chemistry, which parallel petroleum oil both in their chemical structures and pressure-viscosity coefficients. The silicone, ester and polyglycol oils have an oxygen based chemistry that is structurally quite different from petroleum oils and PAO oils. This difference has a profound effect on reductions in bearing fatigue life and increases in bearing wear could result from this reduction of lubricant film thickness.

Item		Lubr- city	Tempe- rature viscosity	Heatre- sisting property	Oxid- ation stability	Rubber compa- tibility	Remarks
Synthetic oil
Mineral oil	Low-viscosity mineral oil						Not recommended for use at high temperatures.
	High-viscosity mineral oil						Not recommended for use at low temperatures.
Ester	Diester						Excellent low-temperature performance; May swell rubber.
	Polyol ester						Performs well over a wide temperature range; May swell rubber.
Synthetic hydrocarbon	Low and medium viscosity hydrocarbon						Performs well over a wide temperature range with little adverse effect on rubber and plastics because of its molecular structure without a polar group.
	High-viscosity hydrocarbon						However, not recommended for natural rubber and EPDM parts.
Polyglycol							Little adverse effect on rubber including natural rubber and EPDM; Shows little electric resistance.
Phenyl ether	Diphenyl ether						Excellent heat and oxidation stabilities and better anti-radiation property.
	Poly phenyl ether						Excellent heat and oxidation stabilities and better anti-radiation property; Low viscosity index, resulting in somewhat poor low-temperature fluidity.
Silicone							Excellent in heat and oxidation stabilities, while somewhat poor in lubricating boundary surface of steel vs. steel.
PFAE	High-viscosity perfluoro alkyl polyether						Has the best heat and oxidation stabilities among all oils available; Excellent in chemical resistance,insoluble in organic solvent, and of low vapor pressure.
	High-VI perfluoro alkyal polyether

:Excellent

:Very good

:Good

:Fair

:Poor