Compressor oils

Compressors are devices that increase the pressure of gas, air, refrigerant gas and other gases, through mechanical energy.
Compressors can be divided into two large families: volumetric (the compression is the result of mechanical movements that reduce the gas volume) and dynamic (the compression is obtained by rotating blades which give the kinetic energy to gas and by fixed blades in the crankcase which accelerate the flow of gas). 
Furthermore, there are different types of refrigeration compressors utilizing different kind of refrigerants gas.

Lubricants are supposed to reduce: friction, minimize wear, ease cooling and act as a barrier against compressed gas avoiding pressure drops.