1. Demulsibility: The ability of a fluid that is insoluble in water to separate from water with which it may be mixed in the form of emulsion. Or it is the oil's ability to release water. 2. Lubricity: it is the measure of the reduction in friction due to use of oil between two surfaces. 3. High flash point: Flash point is a temperature at which liquid catches fire automatically. The flash point of good hydraulic oil must be as high as possible so that fire possibility nullified. 4. Minimum Toxicity: Good hydraulic oil must be minimum toxic to human being working with them. Some fire resistance hydraulic oils are highly toxic which can cause occupational diseases. 5. Low Foaming Tendency: When oil returns to receiver, it comes in contact with air above the liquid surface. The oil has tendency to absorb air or gas which results in foam formation. Good hydraulic oil must release the air/gas very quickly so that it does not form foam. 6. Fire resistance: Good hydraulic oil must be fire resistant to avoid accidents. 7. Viscosity: It is the resistance offered by the liquid to flow. It is inherent property of the liquid and this resistance to flow depends on some other physical properties such as temperature, pressure, etc. 8. Compressibility: It is the ability of a fluid to get compressed and liquids are less compressible. Compressibility is the reciprocal of bulk modulus.