What should be used to lubricate a mechanical chain in industry: Oil or Grease?

It is known that the service life of a conveyor or transmission chain depends on it being properly lubricated. More specifically, the lubricant should insert itself as a thin film between metallic surfaces that come into contact with one another in the chains, and the surfaces between the axles and the sockets, and the surfaces between the plates.
To be able to do this, the lubricant has to be fluid enough to penetrate into the articulations and between the plates, and has to have a high wetting ability: preference should be given to a lubricating oil the viscosity of which varies depending on how it is applied (for example, manually, using a drip system, etc.). 
However, in some cases and / or for some applications, the manufacturer will prescribe the use of greases.
Most of the time, chains operating in a humid atmosphere and / or humid environment (when the manufacturing process involves their total or partial immersion) will need to be lubricated (for example: steriliser in a cannery).

In this case, the chains will be designed to be lubricated using greases - there will be grease channels in the axles so that the surfaces between the axle and the socket can be lubricated - or they will be larger so that surfaces that come into contact with one another can be lubricated using a greased pump.